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__/AuthGate.test.tsx

@@ -5,17 +5,19 @@
  * and a later 401 `EAUTH` brings the login page back. `usePermissions` and
  * `useWorkLanes` mirror the server's roles: an admin changes everything, an
  * analyst reads everything but works only in their own workspaces, a
- * developer only ever sees (and so changes) their own.
+ * developer only ever sees (and so changes) their own. The login page wears the
+ * OS's light/dark; a sign-in swaps in the account's saved appearance.
  * @author Nguyễn Ngọc Trí Vĩ <vinnt@smartgift.vn>
  */
 
 import { describe, it, expect, vi, beforeEach } from "vitest";
-import { act, cleanup, render, screen } from "@testing-library/react";
+import { act, cleanup, render, screen, waitFor } from "@testing-library/react";
 import userEvent from "@testing-library/user-event";
 import "../../i18n";
 
 const me = vi.fn();
 const login = vi.fn();
+const prefs = vi.fn();
 const LANES = [
   { id: 1, owner_id: 5 },
   { id: 2, owner_id: 6 },
@@ -25,6 +27,7 @@ vi.mock("../../lib/api", () => ({
   api: {
     auth: { me: () => me(), login: (u: string, p: string) => login(u, p), logout: vi.fn() },
     lanes: { list: () => Promise.resolve({ lanes: LANES }) },
+    me: { prefs: () => prefs(), savePrefs: () => Promise.resolve({ prefs: {} }) },
   },
 }));
 
@@ -52,6 +55,7 @@ const user = { id: 1, username: "mia", role: "developer" };
 beforeEach(() => {
   me.mockReset();
   login.mockReset();
+  prefs.mockReset().mockResolvedValue({ prefs: {} });
   localStorage.clear();
 });
 
@@ -107,15 +111,15 @@ describe("AuthGate", () => {
     render(<AuthGate>app</AuthGate>);
 
     const name = await screen.findByLabelText(/username/i);
-    const pass = screen.getByLabelText(/password/i);
+    const pass = screen.getByLabelText(/^password$/i);
     await userEvent.type(name, "mia");
     await userEvent.type(pass, "nope");
-    await userEvent.click(screen.getByRole("button"));
+    await userEvent.click(screen.getByRole("button", { name: /sign in/i }));
     expect(await screen.findByRole("alert")).toBeInTheDocument();
     expect(screen.queryByText("app")).toBeNull();
 
     await userEvent.type(pass, "member-pass-1");
-    await userEvent.click(screen.getByRole("button"));
+    await userEvent.click(screen.getByRole("button", { name: /sign in/i }));
     expect(await screen.findByText("app")).toBeInTheDocument();
     expect(login).toHaveBeenLastCalledWith("mia", "member-pass-1");
 
@@ -126,6 +130,32 @@ describe("AuthGate", () => {
   });
 });
 
+describe("AuthGate theme", () => {
+  it("wears the OS theme while signed out and the account's own once signed in", async () => {
+    const html = document.documentElement;
+    // The previous user's choice, left in this browser.
+    localStorage.setItem("theme", "dark");
+    localStorage.setItem("agenthub.theme.dark", "darcula");
+    const mq = { matches: false, addEventListener: vi.fn(), removeEventListener: vi.fn() };
+    vi.stubGlobal("matchMedia", () => mq); // the OS is light
+    me.mockResolvedValue({ mode: "server", user: null });
+    prefs.mockResolvedValue({ prefs: { theme: "dark", "agenthub.theme.dark": "orca-dark" } });
+    login.mockResolvedValue({ user });
+    render(<AuthGate>app</AuthGate>);
+
+    await userEvent.type(await screen.findByLabelText(/username/i), "mia");
+    expect(html.dataset.mode).toBe("light");
+    expect(html.hasAttribute("data-theme")).toBe(false);
+
+    await userEvent.type(screen.getByLabelText(/^password$/i), "member-pass-1");
+    await userEvent.click(screen.getByRole("button", { name: /sign in/i }));
+    await waitFor(() => expect(html.dataset.theme).toBe("orca-dark"));
+    expect(html.dataset.mode).toBe("dark");
+    expect(localStorage.getItem("agenthub.theme.dark")).toBe("orca-dark");
+    vi.unstubAllGlobals();
+  });
+});
+
 describe("usePermissions / useWorkLanes", () => {
   const as = async (state: unknown) => {
     cleanup();