feat(workspace): a session in its own worktree, Claude's way

Desktop-parity phase 6, following Claude Desktop:
- the workspace home's Worktree checkbox starts the pane with
  `claude --worktree=<name>`, so Claude Code makes, populates
  (.worktreeinclude, WorktreeCreate hook) and cleans up
  <repo>/.claude/worktrees/<name>; AgentHub only excludes
  /.claude/worktrees/ at the repo root (Claude does not)
- server/lib/session-worktree.js resolves a session's worktree from the
  session row only (owned by the workspace, registered by git worktree
  list); every lane git route takes ?session= and answers ENOWORKTREE
  instead of falling back to the main folder
- the session view's Changes panel works in the opened run's worktree
  (dashboard_runs.worktree, GitTarget in the client api)
- Resume/Fork start in the session's worktree; a gone one is ENOWORKTREE
- Archive of a worktree session removes the worktree after asking:
  git worktree remove without --force, git branch -d (unmerged work keeps
  its branch), a lock held by a live pid refused, a stale one cleared
- listWorktrees reads `locked <reason>` locks
- tests scrub GIT_* env so the pre-commit suite cannot act on this repo

client/src/components/lanes/__tests__/SessionResumeButton.test.tsx

@@ -43,7 +43,12 @@ function Where() {
   return <span data-testid="where">{loc.pathname + loc.search}</span>;
 }
 
-function renderButton(session: { id: string; cwd: string | null; tool?: string }) {
+function renderButton(session: {
+  id: string;
+  cwd: string | null;
+  tool?: string;
+  lane_id?: number;
+}) {
   return render(
     <MemoryRouter initialEntries={["/sessions/x"]}>
       <Routes>
@@ -136,6 +141,17 @@ describe("SessionResumeButton", () => {
     });
   });
 
+  it("resumes a session in its own worktree through the workspace that owns it", async () => {
+    const user = userEvent.setup();
+    renderButton({ id: "s-wt", cwd: "/r/.claude/worktrees/ah-3-x", tool: "claude", lane_id: 3 });
+    await user.click(await screen.findByRole("button", { name: "Resume" }));
+    await user.click(screen.getByRole("button", { name: "Resume session" }));
+    expect(api.lanes.action).toHaveBeenCalledWith(3, "start", {
+      slot: 1,
+      resumeSessionId: "s-wt",
+    });
+  });
+
   it("offers no Resume for a session started in a subfolder, but opens its live pane", async () => {
     const { unmount } = renderButton({ id: "s-9", cwd: "/r/lib", tool: "claude" });
     await waitFor(() => expect(api.run.list).toHaveBeenCalled());