feat(workspace): session view console as tabs, with New terminal

The 1/2/4 split view becomes a tab bar (ConsoleTabs.tsx): one tab per live
tmux slot (0-3) of the workspace, the active one being ?run=, every live tab's
pane kept mounted and hidden with CSS. The + menu opens a new tab in the first
free slot: New terminal (a plain shell - shell: true on POST
/api/lanes/:id/start, spawnShell, tool 'shell', no run_id/status change), any
installed enabled AI tool started bare, or Settings -> Agents. A tab's x stops
its session. splitViewStorage, &pane= and the sidebar's Ctrl/Cmd+click are gone.

client/src/components/run/LaneConsolePane.tsx

@@ -2,10 +2,11 @@
  * @file LaneConsolePane.tsx
  * @description One lane's run console: a TerminalView on the pane's tmux
  * session, or — with no run — an empty pane whose button goes back to the
- * workspace home, the ONE place a new session is started (its prompt box,
- * `WorkspaceHome.tsx`; there is no run form in a pane any more). Moved out of
- * Workspace.tsx so the Workspace page can render 1, 2, or 4 of these side by
- * side (split terminal view). Owns its own handle/busy/runHistory state —
+ * workspace home, where a session starts with a prompt (its prompt box,
+ * `WorkspaceHome.tsx`; there is no run form in a pane — the tab bar's `+`,
+ * `ConsoleTabs.tsx`, starts a bare CLI or a shell). Moved out of
+ * Workspace.tsx so the Workspace page can keep one per TAB (slot 0–3) mounted,
+ * the inactive ones hidden with CSS. Owns its own handle/busy/runHistory state —
  * nothing is shared between panes. `lanes`, `binaryStatus`, `activeRuns`, and
  * `externalSessions` are supplied as props because they are global, not
  * lane-specific, and fetching them per pane would mean N redundant identical
@@ -16,8 +17,8 @@
  * and its live tmux session — instead of leaving the previous lane's terminal
  * on screen under a new lane's header.
  *
- * Each pane is one tmux session on its lane — split panes all show the same
- * lane, pane `slot` N owning `agenthub-lane-<id>[-N]` — so starting or resuming
+ * Each pane is one tmux session on its lane — every tab shows the same
+ * lane, tab `slot` N owning `agenthub-lane-<id>[-N]` — so starting or resuming
  * into a pane already holding a live run answers 409 ERUNLIVE rather than overwriting a
  * prompt in flight — `onResumeFromHistory` catches
  * that and attaches to the still-live session instead of failing outright
@@ -65,7 +66,7 @@ export interface LaneConsolePaneProps {
   externalSessions?: Session[];
   wsConnected: boolean;
   onHasActiveRunChange?: (active: boolean) => void;
-  /** Which split pane this is. Every pane shows the SAME lane, each in its own
+  /** Which tab this is. Every tab shows the SAME lane, each in its own
    *  tmux session: slot 0 is the lane's own, 1–3 are `agenthub-lane-<id>-<slot>`. */
   slot?: number;
   /** Runs the OTHER panes are showing — left out of this pane's Active runs so
@@ -78,8 +79,8 @@ export interface LaneConsolePaneProps {
   attachRequest?: { runId: string; nonce: string } | null;
   /** Opens the workspace home, where a new session is started. */
   onNewSession?: () => void;
-  /** The pane's run exiting goes back to the home too (a single pane). */
-  homeOnExit?: boolean;
+  /** The pane's run exited (the tab bar opens another tab, or the home). */
+  onRunExit?: () => void;
 }
 
 /** The tmux session a lane's split pane owns (see server/lib/pty-run.js). */
@@ -103,7 +104,7 @@ export function LaneConsolePane({
   onHandleChange,
   attachRequest,
   onNewSession,
-  homeOnExit = false,
+  onRunExit,
 }: LaneConsolePaneProps) {
   const { t } = useTranslation("run");
   const { t: tLanes } = useTranslation("lanes");
@@ -490,12 +491,12 @@ export function LaneConsolePane({
             runId={handle!.id}
             wsBaseUrl={window.location.origin.replace(/^http/, "ws")}
             // The pane died (double Ctrl+C out of `claude`, `exit`, a crash) —
-            // a single pane goes straight back to the home's prompt box rather
-            // than leaving a dead terminal the user has to click out of.
+            // the tab bar moves on (another tab, or the home's prompt box)
+            // rather than leaving a dead terminal the user has to click out of.
             onExit={() => {
               newRun();
               refreshList();
-              if (homeOnExit) onNewSession?.();
+              onRunExit?.();
             }}
           />
           <button