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/lanes/LaneGitBar.tsx

@@ -45,14 +45,7 @@ import { isSubmitEnter } from "../../lib/keys";
 import type { LaneGitFacts, LaneWorktree } from "../../lib/types";
 
 type Action =
-  | "fetch"
-  | "pull"
-  | "push"
-  | "switch"
-  | "branch-create"
-  | "branch-delete"
-  | "merge"
-  | "publish";
+  "fetch" | "pull" | "push" | "switch" | "branch-create" | "branch-delete" | "merge" | "publish";
 type RunBody = Parameters<typeof api.lanes.gitAction>[2];
 
 const LOCAL_HOST = /^(localhost|127\.|\[::1\])/;
@@ -95,6 +88,7 @@ function Btn({
 export function LaneGitBar({
   laneId,
   session,
+  source,
   git,
   onChanged,
   onNewLane,
@@ -103,6 +97,8 @@ export function LaneGitBar({
   laneId: number;
   /** Work in that session's own worktree (see `gitTarget`). */
   session?: string;
+  /** Work in that extra folder's repo instead (`lane_sources` id, see `gitTarget`). */
+  source?: number;
   git: LaneGitFacts;
   /** Rendered at the start of the action row: the header's branch line, so
    *  the facts and the buttons that act on them read as one row. */
@@ -165,7 +161,7 @@ export function LaneGitBar({
     setBusy(action);
     setError(null);
     try {
-      const res = await api.lanes.gitAction(gitTarget(lane, session), action, body || {});
+      const res = await api.lanes.gitAction(gitTarget(lane, session, source), action, body || {});
       // Landed after a lane switch: every write below belongs to the lane
       // no longer shown.
       if (laneNow.current !== lane) return;
@@ -218,7 +214,7 @@ export function LaneGitBar({
 
   const refreshBranches = async () => {
     try {
-      const r = await api.lanes.gitBranches(gitTarget(laneId, session));
+      const r = await api.lanes.gitBranches(gitTarget(laneId, session, source));
       if (laneNow.current !== laneId) return;
       setBranches(r.branches);
       setWorktrees(r.worktrees || []);