feat: v2.6.0 — Chat UI composer (+ menu, project files, activity panel, permission mode, Stop), git on a workspace's extra folders (#70), long paste as a file (#68), S3 server mode (experimental)

Chat UI:
- Each Claude/Codex session keeps its own chat/terminal view; Settings only
  sets how new sessions open.
- Composer + menu: upload, project files and folders (#54, also dragged from
  the Files/Changes tree), context files, recent uploads, skills, plugins.
- Activity side panel (progress, outputs, files read, uploads, memory,
  skills, connectors) with a file preview; edited-file counts per turn.
- Permission-mode chip (Shift+Tab steps, read back from the pane:
  server/lib/pane-mode.js, GET|POST /api/run/:id/permission-mode).
- Stop (Esc) while the main agent works; the status is checked per agent
  (with session_id /api/agents ignores its status filter) and re-read every
  5 s while Stop shows.
- Dropped images shown in the conversation (GET /api/run/drop/:name, the
  requester's own drop dir), full-size viewer.
- A plain-text paste over 5,000 characters is attached as pasted-text.txt,
  so no prompt reaches tmux/argv limits (#68).

Changes panel: every /api/lanes/:id/git* route takes ?source=<lane_sources
id> (sourceFolder; ENOSOURCE otherwise) and a folder picker switches the
whole panel to a workspace's extra folder (#70).

Server mode S3 (one Linux user per account) — experimental, verified with
fake sudo plus a P6 managed-settings spike on a test account:
- member tmux listing runs in the background (cached, 15 s => unknown);
- transcript snapshot copy is async, chunked, temp file + rename;
- Express Layer patch only on Express 4;
- tmux capturePane/sendKey go to the member's own server.

Docs: the multi-user design moved in as docs/plans/server-mode/README.md
(the AgentHub-Server repo is gone); S3-PLAN P6 result; LANES/API/openapi.

client/src/components/lanes/AddLaneModal.tsx

@@ -10,7 +10,8 @@
  * (Claude Code or Codex) — this choice is immutable after creation. Either
  * mode's path field can be filled by typing, by the CwdAutocomplete
  * suggestions, or by Browse (`PathPickButton`: the OS's own folder picker
- * opened by the server, the in-app `FolderBrowseModal` where it cannot be).
+ * opened by the server, the in-app `FolderBrowseModal` where it cannot be) —
+ * which a click into the field opens too.
  * The worktree lane returned is `status: "provisioning"`:
  * the route answers before the actual `git worktree add` runs, so this
  * component polls `GET /api/lanes/:id` until that finishes before running the
@@ -327,6 +328,7 @@ export function AddLaneModal({
   const titleId = useId();
   const panelRef = useRef<HTMLDivElement>(null);
   const cancelRef = useRef<HTMLButtonElement>(null);
+  const browseRef = useRef<HTMLButtonElement>(null);
   useDialog(open, panelRef, handleCancel, cancelRef);
 
   // A summary on screen means the lane already exists and a step failed, so
@@ -459,7 +461,14 @@ export function AddLaneModal({
               {mode === "repo" ? t("addLaneRepoLabelAdopt") : t("addLaneRepoLabel")}
             </label>
             <div className="flex gap-1.5" data-tour="add-lane-folder">
-              <div className="min-w-0 flex-1">
+              {/* A click into the path opens the picker, as Browse does (the
+                OS's own where it can be); typing still works from the keyboard. */}
+              <div
+                className="min-w-0 flex-1"
+                onClick={(e) => {
+                  if ((e.target as HTMLElement).tagName === "INPUT") browseRef.current?.click();
+                }}
+              >
                 <CwdAutocomplete
                   inputId="add-lane-repo"
                   value={sourceRepo}
@@ -467,7 +476,12 @@ export function AddLaneModal({
                   suggestions={cwdSuggestions}
                 />
               </div>
-              <PathPickButton start={sourceRepo} onPick={setSourceRepo} showLabel />
+              <PathPickButton
+                start={sourceRepo}
+                onPick={setSourceRepo}
+                showLabel
+                buttonRef={browseRef}
+              />
             </div>
             <p className="mt-1 text-[10px] text-fg-muted">
               {mode === "repo" ? t("addLaneRepoHintAdopt") : t("addLaneRepoHint")}