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/__tests__/WorkspaceTree.test.tsx

@@ -53,6 +53,11 @@ vi.mock("../../lib/api", async (importOriginal) => {
         list: vi.fn(async () => ({ lanes, counts: {} })),
         update: vi.fn(async () => ({ lane: lanes[0] })),
         action: vi.fn(async () => ({ ok: true })),
+        removeSessionWorktree: vi.fn(async () => ({
+          removed: true,
+          branch: "x",
+          branchKept: false,
+        })),
         routerList: vi.fn(async () => ({ routers: [] })),
       },
       sessions: {
@@ -158,6 +163,50 @@ describe("WorkspaceTree", () => {
     expect(api.sessions.patch).toHaveBeenCalledWith("s-live", { archived: true });
   });
 
+  it("archiving a worktree session removes its worktree first, after asking", async () => {
+    vi.mocked(api.sessions.list).mockImplementation(async () => ({
+      sessions: [
+        { ...session("s-wt", "In a worktree"), cwd: "/r/.claude/worktrees/ah-1-x" } as Session,
+      ],
+      total: 1,
+      limit: 20,
+      offset: 0,
+    }));
+    const user = userEvent.setup();
+    renderTree();
+    await user.click(await screen.findByTestId("workspace-toggle-1"));
+    expect(await screen.findByTestId("workspace-session-worktree-s-wt")).toBeInTheDocument();
+    await user.click(screen.getByTestId("workspace-session-archive-s-wt"));
+    expect(api.sessions.patch).not.toHaveBeenCalled();
+    expect(screen.getByRole("dialog")).toHaveTextContent(".claude/worktrees/ah-1-x");
+    await user.click(screen.getByRole("button", { name: "Archive and remove" }));
+    await waitFor(() =>
+      expect(api.sessions.patch).toHaveBeenCalledWith("s-wt", { archived: true })
+    );
+    expect(api.lanes.removeSessionWorktree).toHaveBeenCalledWith(1, "s-wt");
+  });
+
+  it("keeps a worktree session when git refuses to remove its worktree", async () => {
+    vi.mocked(api.sessions.list).mockImplementation(async () => ({
+      sessions: [
+        { ...session("s-wt", "In a worktree"), cwd: "/r/.claude/worktrees/ah-1-x" } as Session,
+      ],
+      total: 1,
+      limit: 20,
+      offset: 0,
+    }));
+    vi.mocked(api.lanes.removeSessionWorktree).mockRejectedValueOnce(
+      Object.assign(new Error("contains modified or untracked files"), { code: "EGIT" })
+    );
+    const user = userEvent.setup();
+    renderTree();
+    await user.click(await screen.findByTestId("workspace-toggle-1"));
+    await user.click(await screen.findByTestId("workspace-session-archive-s-wt"));
+    await user.click(screen.getByRole("button", { name: "Archive and remove" }));
+    expect(await screen.findByRole("alert")).toHaveTextContent("modified or untracked");
+    expect(api.sessions.patch).not.toHaveBeenCalled();
+  });
+
   it("dots a session waiting for the user amber and a failed one red", async () => {
     vi.mocked(api.sessions.list).mockImplementation(async () => ({
       sessions: [