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.

server/routes/me.js

@@ -1,13 +1,15 @@
 /**
  * @file me.js
- * @description `/api/me` — the signed-in account's own UI preferences and its
- * first-run setup (docs/plans/onboarding). The browser keeps these in
- * localStorage; this stores the same keys per ACCOUNT (`user_prefs`), so they
- * follow it to any browser and the setup wizard shows once per account.
- * Local mode is one account, `local`. Only the keys in `PREF_KEYS` are kept,
- * each a string of at most 8 KB — this is a preferences store, not a blob
- * store. Writes are same-origin and touch only the caller's own row.
- * `agenthub.chatUi` ("1") opens Claude/Codex sessions as a chat (`PaneChat`).
+ * @description `/api/me` — the signed-in account's own UI preferences
+ * (`user_prefs`) and its first-run setup (docs/plans/onboarding), so they
+ * follow it to any browser, differ between the accounts of one dashboard, and
+ * the setup wizard shows once per account. Local mode is one account,
+ * `local`; server mode keys a row `u<id>` by the login cookie — the request
+ * never names an account. Only the keys in `PREF_KEYS` are kept, each a
+ * string of at most 8 KB, and a PUT merges into the row (`null` removes a
+ * key). Writes are same-origin and touch only the caller's own row.
+ * `agenthub.chatUi` ("1") opens Claude/Codex sessions as a chat (`PaneChat`);
+ * the appearance keys are `useTheme`'s own (`theme`, `agenthub.theme.dark|light`).
  *
  * S3 (one Linux user per account): an account's dark/light choice also becomes
  * the theme in their own Claude Code settings, written as them.
@@ -92,7 +94,10 @@ router.put("/prefs", sameOriginGuard, (req, res) => {
     }
     if (v === null) delete prefs[k];
     else if (typeof v === "string" && v.length <= MAX_VALUE) prefs[k] = v;
-    else return res.status(400).json({ error: { code: "EBADPREFS", message: `${k}: a short string` } });
+    else
+      return res
+        .status(400)
+        .json({ error: { code: "EBADPREFS", message: `${k}: a short string` } });
   }
   upsert.run(key, JSON.stringify(prefs));
   if ("theme" in patch) followClaudeTheme(req, patch.theme);