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/__tests__/Select.test.tsx

@@ -2,7 +2,8 @@
  * @file Select.test.tsx
  * @description The shared Select as a WAI-ARIA listbox button: expanded state,
  * listbox/option roles with aria-selected, aria-activedescendant tracking,
- * Arrow/Home/End/Enter/Escape/type-ahead, and focus back on the trigger.
+ * Arrow/Home/End/Enter/Escape/type-ahead, focus back on the trigger, and a
+ * list that flips up by the room in its split pane, not the window's.
  * @author Nguyễn Ngọc Trí Vĩ <vinnt@smartgift.vn>
  */
 
@@ -90,4 +91,21 @@ describe("Select (listbox button)", () => {
     fireEvent.click(screen.getByText("Apple"));
     expect(onChange).toHaveBeenCalledWith("a");
   });
+
+  it("opens upward when its pane (data-menu-bounds) has no room below, whatever the window has", () => {
+    const rect = (top: number, bottom: number) => ({ top, bottom }) as DOMRect;
+    render(
+      <div data-menu-bounds data-testid="pane">
+        <Select value="b" onChange={() => {}} options={OPTIONS} label="Fruit" />
+      </div>
+    );
+    // A top pane 0–400 in a 2000px window; the trigger near its bottom.
+    vi.spyOn(screen.getByTestId("pane"), "getBoundingClientRect").mockReturnValue(rect(0, 400));
+    const button = screen.getByRole("button", { name: "Fruit" });
+    vi.spyOn(button, "getBoundingClientRect").mockReturnValue(rect(360, 380));
+    vi.stubGlobal("innerHeight", 2000);
+    fireEvent.click(button);
+    expect(screen.getByRole("listbox").className).toContain("bottom-full");
+    vi.unstubAllGlobals();
+  });
 });