feat: workspaces own their sessions; desktop parity; sidebar and settings cleanup

Workspace sessions (docs/plans/desktop-parity, phases 1-5 and 7):
- sessions.lane_id: a workspace lists only the sessions its panes held,
  stamped by bindRunSession (first writer wins, nested `claude -p`
  excluded); GET /api/sessions?lane=&archived=
- session row state dot, double-click rename, archive (sessions.archived_at,
  hides only); the activity bar's duplicate Sessions tab removed
- Fork beside Resume (--fork-session, Claude only), Ctrl/Cmd+click a live
  session opens it in a second pane, a diff line's comment is pasted into
  the workspace's last-focused pane (lib/panePaste.ts)

dashboard_runs stability:
- a pane's previous run is archived as <pane>@<started_at> instead of being
  overwritten by INSERT OR REPLACE
- a run is flagged abandoned only once its tmux session is gone, at boot and
  on the run-heal beat (panes outlive a server restart)

UI:
- sidebar: no footer, language or theme block; small collapse button in the
  brand corner; version + update check in the connection details modal, a
  status-bar dot while a release is out; language in Settings -> General
- one Switch component for every switch, the themed Checkbox for every
  checkbox (no native checkboxes)

Also: AI Tools catalog trimmed to 10 built-ins (custom-file prompt modes
tested through fixtures), and the workspace plans under docs/plans/ (the
multi-user server plan lives in the AgentHub-Server repo).

client/src/components/lanes/LaneDiffView.tsx

@@ -262,7 +262,28 @@ export function analyseHunk(hunk: LaneDiffHunk): Analysed {
   return out;
 }
 
-function Gutter({ n }: { n: number | null }) {
+/** Set by a LaneDiffView given `onComment`: a click on a NEW line's number
+ *  opens the comment box for that line. */
+const CommentLine = createContext<{
+  open: (line: number) => void;
+  title: (line: number) => string;
+} | null>(null);
+
+function Gutter({ n, commentable = false }: { n: number | null; commentable?: boolean }) {
+  const comment = useContext(CommentLine);
+  if (commentable && comment && n != null) {
+    return (
+      <button
+        type="button"
+        data-testid={`diff-comment-line-${n}`}
+        onClick={() => comment.open(n)}
+        title={comment.title(n)}
+        className="w-10 shrink-0 select-none px-1 text-right text-fg-muted/60 hover:bg-accent/20 hover:text-accent"
+      >
+        {n}
+      </button>
+    );
+  }
   return (
     <span className="w-10 shrink-0 select-none px-1 text-right text-fg-muted/60">{n ?? ""}</span>
   );
@@ -462,7 +483,7 @@ function UnifiedLine({
   return (
     <Row tint={rowTint(line.type)} style={style} anchor={anchor}>
       <Gutter n={line.oldLine} />
-      <Gutter n={line.newLine} />
+      <Gutter n={line.newLine} commentable />
       <span className="whitespace-pre px-2">
         <span className={`select-none ${markerClass(line.type)}`}>
           {line.type === "add" ? "+" : line.type === "del" ? "-" : " "}
@@ -534,7 +555,10 @@ function SplitLine({
   const anchor = useAnchor(start);
   return (
     <Row tint={rowTint(line?.type ?? null)} style={style} anchor={anchor}>
-      <Gutter n={(side === "left" ? line?.oldLine : line?.newLine) ?? null} />
+      <Gutter
+        n={(side === "left" ? line?.oldLine : line?.newLine) ?? null}
+        commentable={side === "right"}
+      />
       <span className="whitespace-pre px-1">
         {line ? (
           <Code
@@ -700,6 +724,7 @@ export function LaneDiffView({
   layout,
   fill = false,
   hunkActions,
+  onComment,
 }: {
   file: LaneChangeFile;
   layout: DiffLayout;
@@ -707,9 +732,35 @@ export function LaneDiffView({
   fill?: boolean;
   /** Controls drawn in each change block's review bar. */
   hunkActions?: (change: LaneDiffChange) => ReactNode;
+  /** Makes each new line's number a button that writes a comment on that line
+   *  and hands `<path>:<line> — <text>` here; false = it reached no pane. */
+  onComment?: (text: string) => boolean;
 }) {
   const root = useRef<HTMLDivElement>(null);
   const { t } = useTranslation(["lanes"]);
+  const [commentAt, setCommentAt] = useState<number | null>(null);
+  const [draft, setDraft] = useState("");
+  const [undelivered, setUndelivered] = useState(false);
+  const openComment = useMemo(
+    () =>
+      onComment
+        ? {
+            open: (line: number) => {
+              setCommentAt(line);
+              setUndelivered(false);
+            },
+            title: (line: number) => t("changes.commentLine", { n: line }),
+          }
+        : null,
+    [onComment, t]
+  );
+  const sendComment = () => {
+    const text = draft.trim();
+    if (!text || commentAt == null || !onComment) return;
+    if (!onComment(`${file.path}:${commentAt} — ${text}`)) return setUndelivered(true);
+    setCommentAt(null);
+    setDraft("");
+  };
   const lang = langFor(file.path);
   const hunks = file.hunks;
   const items = useMemo(() => (hunks ? flatten(hunks, "unified") : []), [hunks]);
@@ -755,50 +806,96 @@ export function LaneDiffView({
     return <p className="px-2 py-1 text-[10px] text-fg-muted">{t("changes.noHunks")}</p>;
 
   return (
-    <HunkActions.Provider value={review}>
-      <div
-        ref={root}
-        data-testid="lane-diff-view"
-        data-layout={layout}
-        onScroll={(e) => win.onScroll(e.currentTarget)}
-        className={`flex flex-col font-mono text-[11px] leading-[1.45] ${
-          layout === "split"
-            ? boxHeight(fill, splitWindowed)
-            : `overflow-auto ${boxHeight(fill, win.on)}`
-        }`}
-      >
-        {layout === "split" ? (
-          <SplitView hunks={file.hunks} lang={lang} fill={fill} />
-        ) : win.on ? (
-          <Windowed count={items.length} range={win.range} minWidth={minWidth}>
-            {items
-              .slice(win.range.start, win.range.end)
-              .map(({ hunk, i }, k) =>
-                i < 0 ? (
-                  <HunkHeader key={win.range.start + k} hunk={hunk} fixed />
-                ) : (
-                  <UnifiedLine
-                    key={win.range.start + k}
-                    line={hunk.lines[i]!}
-                    lang={lang}
-                    emph={analyseHunk(hunk).emph.get(i)}
-                    style={FIXED}
-                    bar={barAtLine(hunk, i)}
-                    start={startAtLine(hunk, i)}
-                  />
-                )
-              )}
-          </Windowed>
-        ) : (
-          file.hunks.map((hunk, i) => (
-            <UnifiedHunk key={`${hunk.header}:${i}`} hunk={hunk} lang={lang} />
-          ))
+    <CommentLine.Provider value={openComment}>
+      <HunkActions.Provider value={review}>
+        <div
+          ref={root}
+          data-testid="lane-diff-view"
+          data-layout={layout}
+          onScroll={(e) => win.onScroll(e.currentTarget)}
+          className={`flex flex-col font-mono text-[11px] leading-[1.45] ${
+            layout === "split"
+              ? boxHeight(fill, splitWindowed)
+              : `overflow-auto ${boxHeight(fill, win.on)}`
+          }`}
+        >
+          {layout === "split" ? (
+            <SplitView hunks={file.hunks} lang={lang} fill={fill} />
+          ) : win.on ? (
+            <Windowed count={items.length} range={win.range} minWidth={minWidth}>
+              {items
+                .slice(win.range.start, win.range.end)
+                .map(({ hunk, i }, k) =>
+                  i < 0 ? (
+                    <HunkHeader key={win.range.start + k} hunk={hunk} fixed />
+                  ) : (
+                    <UnifiedLine
+                      key={win.range.start + k}
+                      line={hunk.lines[i]!}
+                      lang={lang}
+                      emph={analyseHunk(hunk).emph.get(i)}
+                      style={FIXED}
+                      bar={barAtLine(hunk, i)}
+                      start={startAtLine(hunk, i)}
+                    />
+                  )
+                )}
+            </Windowed>
+          ) : (
+            file.hunks.map((hunk, i) => (
+              <UnifiedHunk key={`${hunk.header}:${i}`} hunk={hunk} lang={lang} />
+            ))
+          )}
+          {file.truncated && (
+            <p className="px-2 py-1 text-[10px] text-status-warning">
+              {t("changes.fileTruncated")}
+            </p>
+          )}
+        </div>
+        {commentAt != null && (
+          <form
+            data-testid="diff-comment-box"
+            className="flex flex-col gap-1 border-t border-border bg-surface-2 p-2"
+            onSubmit={(e) => {
+              e.preventDefault();
+              sendComment();
+            }}
+          >
+            <label className="text-[11px] text-fg-muted">
+              {t("changes.commentOn", { at: `${file.path}:${commentAt}` })}
+              <textarea
+                autoFocus
+                rows={2}
+                value={draft}
+                onChange={(e) => setDraft(e.target.value)}
+                onKeyDown={(e) => {
+                  if (e.key === "Escape") setCommentAt(null);
+                  if (e.key === "Enter" && (e.ctrlKey || e.metaKey)) sendComment();
+                }}
+                className="mt-1 block w-full rounded border border-border bg-surface-1 px-2 py-1 font-sans text-xs text-fg-primary"
+              />
+            </label>
+            {undelivered && (
+              <p role="alert" className="text-[11px] text-status-danger">
+                {t("changes.commentNoPane")}
+              </p>
+            )}
+            <div className="flex justify-end gap-2">
+              <button
+                type="button"
+                className="btn-ghost text-xs"
+                onClick={() => setCommentAt(null)}
+              >
+                {t("changes.commentCancel")}
+              </button>
+              <button type="submit" className="btn-primary text-xs" disabled={!draft.trim()}>
+                {t("changes.commentSend")}
+              </button>
+            </div>
+          </form>
         )}
-        {file.truncated && (
-          <p className="px-2 py-1 text-[10px] text-status-warning">{t("changes.fileTruncated")}</p>
-        )}
-      </div>
-    </HunkActions.Provider>
+      </HunkActions.Provider>
+    </CommentLine.Provider>
   );
 }