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/lib/__tests__/panePaste.test.ts

@@ -3,12 +3,13 @@
  * @description Pins where a pasted diff comment lands: the workspace's pane
  * focused last, else any of its panes, never another workspace's (lane 1 is
  * not lane 12), nowhere once the pane unmounted, and never into a pane that
- * is not on screen (a hidden console behind a full-width Changes panel).
+ * is not on screen (a hidden console behind a full-width Changes panel); and
+ * `interruptRun`, the Chat view's Stop, presses Esc only in a visible pane.
  * @author Nguyễn Ngọc Trí Vĩ <vinnt@smartgift.vn>
  */
 
 import { describe, expect, it } from "vitest";
-import { notePaneFocus, pasteToLane, registerPane } from "../panePaste";
+import { interruptRun, notePaneFocus, pasteToLane, registerPane } from "../panePaste";
 
 describe("panePaste", () => {
   it("pastes into the workspace's last-focused pane, and only its own", () => {
@@ -48,4 +49,20 @@ describe("panePaste", () => {
     expect(got).toEqual(["y"]);
     off();
   });
+
+  it("interruptRun presses Esc in a visible pane only", () => {
+    const keys: string[] = [];
+    let shown = false;
+    const off = registerPane(
+      "agenthub-lane-6",
+      () => {},
+      () => shown,
+      (d) => keys.push(d)
+    );
+    expect(interruptRun("agenthub-lane-6")).toBe(false);
+    shown = true;
+    expect(interruptRun("agenthub-lane-6")).toBe(true);
+    expect(keys).toEqual(["\x1b"]);
+    off();
+  });
 });