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/WorkspaceHome.tsx

@@ -5,7 +5,8 @@
  * then opens it (`&run=<runId>`) — the one place a session starts WITH a
  * prompt (the session view's tab bar `+` only starts a bare CLI or a shell,
  * `ConsoleTabs.tsx`). Inside
- * the box, like Claude Desktop's: AI (the session's own tool, the workspace's
+ * the box, like Claude Desktop's: the `+` menu (`ChatAddMenu`: upload, or
+ * attach a project file, a context file or a recent upload), AI (the session's own tool, the workspace's
  * by default; its last row, **Open terminal**, is no AI — it starts a plain
  * shell tab at once, like the tab bar's New terminal) and one Model chip (`ModelMenu`: the tool's own list or the
  * proxy's models, plus Effort); under it the quieter choices — AI Proxy
@@ -59,6 +60,8 @@ import { fmtCost, timeAgo } from "../../lib/format";
 import { useAiTools } from "../../hooks/useAiTools";
 import { useProjectTreePrefs } from "../../lib/projectTreePrefs";
 import { ModelMenu, PromptEditor, promptWithImages, type PromptImage } from "../run/RunSetup";
+import { ChatAddMenu } from "../run/ChatAddMenu";
+import { addAttachments } from "../../lib/promptAttach";
 import { AiToolIcon } from "../AiToolIcon";
 import { ProxyPicker, proxyArg, useAiProxies, useSessionProxy } from "../run/ProxyPicker";
 import { Select } from "../Select";
@@ -115,12 +118,15 @@ function HomeBody({
   lane,
   onMenuAction,
   onRenamed,
+  onSourcesChange,
 }: {
   lane: Lane;
   /** Row-menu items the page carries out (its modals); rename is done here. */
   onMenuAction: (action: WorkspaceMenuAction) => void;
   /** Called after a rename, so the page re-reads the lane list. */
   onRenamed?: () => void;
+  /** Called with the sources after a folder or file is added or removed. */
+  onSourcesChange?: (view: LaneSourcesView) => void;
 }) {
   const { t } = useTranslation("lanes");
   const navigate = useNavigate();
@@ -149,6 +155,7 @@ function HomeBody({
     }
   }, [draftKey, prompt]);
   const [images, setImages] = useState<PromptImage[]>([]);
+  const pickFiles = useRef<(() => void) | null>(null);
   const [proxy, setProxy] = useSessionProxy();
   const proxies = useAiProxies();
   // Claude and Codex, also before the catalog has loaded (as ProxyPicker).
@@ -310,7 +317,9 @@ function HomeBody({
   const run = async (fn: () => Promise<LaneSourcesView>) => {
     setError(null);
     try {
-      setView(await fn());
+      const next = await fn();
+      setView(next);
+      onSourcesChange?.(next);
       return true;
     } catch (err) {
       setError(message(err));
@@ -535,9 +544,18 @@ function HomeBody({
             images={images}
             onImagesChange={setImages}
             onBusyChange={setUploading}
+            pickFiles={pickFiles}
             bare
           />
           <div className="mt-1 flex items-center gap-1">
+            <ChatAddMenu
+              cwd={lane.cwd}
+              laneId={lane.id}
+              skills={claude}
+              onUpload={() => pickFiles.current?.()}
+              onInsert={(cmd) => setPrompt((p) => `${cmd} ${p.replace(/^\s+/, "")}`)}
+              onAttach={(items) => setImages((prev) => addAttachments(prev, items))}
+            />
             <div data-testid="workspace-home-tool">
               <Select<string>
                 variant="ghost"