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/hooks/useLanes.ts

@@ -7,7 +7,8 @@
  * frames missed while disconnected are never replayed. The copy is dropped
  * when the last component unmounts, so a fresh mount always reads fresh rows.
  * `useWorkLanes()` is the same list narrowed to the workspaces this user may
- * work in (server mode: an analyst's own), for the Workspace page and tree.
+ * work in (server mode: an analyst's own), for the Workspace page; the sidebar
+ * tree lists them all, other users' read only.
  * @author Nguyễn Ngọc Trí Vĩ <vinnt@smartgift.vn>
  */
 
@@ -97,10 +98,10 @@ export function useLanes() {
 }
 
 /**
- * The workspaces this user WORKS in — the Workspace page and its sidebar tree.
+ * The workspaces this user WORKS in — the Workspace page.
  * Server mode: an analyst gets every workspace from the API (to read) but may
  * change only their own, so only those are listed here; other users' work is
- * read on the Sessions, Analytics and Users pages.
+ * read in the sidebar tree (read only), and on Sessions, Analytics and Users.
  */
 export function useWorkLanes() {
   const all = useLanes();