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/Sidebar.tsx

@@ -74,6 +74,7 @@ import {
 } from "lucide-react";
 import type { LucideIcon } from "lucide-react";
 import { api } from "../lib/api";
+import { BRAND_LOGO, BRAND_MARK } from "../lib/brand";
 import { useAuth, usePermissions } from "./AuthGate";
 import { eventBus } from "../lib/eventBus";
 import { WorkspaceTree } from "./WorkspaceTree";
@@ -88,13 +89,6 @@ const NAV_KEYS = [
   { to: "/sessions", icon: FolderOpen, key: "nav:sessions" },
 ] as const;
 
-// SmartGift wordmark, replacing the old text subtitle. Remote URLs: the logo is
-// owned by the brand, not vendored here — a machine with no network shows the
-// alt text instead.
-const BRAND_LOGO =
-  "https://smg-services.s3.ap-southeast-1.amazonaws.com/smartgift/assets/logo/logo-main.png";
-const BRAND_MARK = "https://smartgift.vn/favicon.ico";
-
 const STORAGE_KEY = "sidebar-collapsed";
 const STATS_STORAGE_KEY = "sidebar-connection-stats";
 const RECENT_EVENTS_CAP = 8;
@@ -496,6 +490,7 @@ export function Sidebar({
             <button
               type="button"
               onClick={onToggle}
+              data-testid="sidebar-tree-rail"
               title={t("lanes:tree.title")}
               aria-label={t("lanes:tree.title")}
               className="flex w-full items-center justify-center rounded-md px-2 py-2 text-fg-secondary transition-colors hover:bg-surface-3 hover:text-fg-primary"