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/onboarding/OnboardingTour.tsx

@@ -7,7 +7,8 @@
  * the real UI); a step moves on when what it asked for has happened (the
  * dialog opened, the workspace exists, the session started), and steps back
  * when the user backed out (the dialog closed with nothing made). Targets are
- * existing `data-testid`s plus three `data-tour` marks in AddLaneModal. The
+ * existing `data-testid`s plus `data-tour` marks in AddLaneModal and
+ * FolderBrowseModal. The
  * step reached is `localStorage["agenthub.tour"]`, so it is synced to the
  * account and survives a reload; `done` ends it.
  * @author Nguyễn Ngọc Trí Vĩ <vinnt@smartgift.vn>
@@ -45,12 +46,14 @@ const STEPS: Record<
   { target: () => Element | null; next?: () => StepId | null; info?: boolean }
 > = {
   add: {
+    // The sidebar's +; folded to a rail, its tree icon (which unfolds it).
     target: () =>
-      shown('[data-testid="lane-empty"]') || shown('[data-testid="workspace-tree-add"]'),
+      shown('[data-testid="workspace-tree-add"]') || shown('[data-testid="sidebar-tree-rail"]'),
     next: () => (modalOpen() ? "folder" : null),
   },
   folder: {
-    target: () => $('[data-tour="add-lane-folder"]'),
+    // The folder browser while it is open: it sits over the field.
+    target: () => $('[data-tour="folder-browse"]') || $('[data-tour="add-lane-folder"]'),
     next: () => (modalOpen() ? null : composer() ? "prompt" : "add"),
     info: true,
   },
@@ -113,7 +116,19 @@ export function OnboardingTour() {
       const moved = def.next?.();
       if (moved && moved !== step) return write(moved);
       const el = def.target();
-      const r = el ? el.getBoundingClientRect() : null;
+      let r = el ? el.getBoundingClientRect() : null;
+      // The folder field's suggestions hang below it: light them too.
+      const list = el?.querySelector("[data-cwd-suggestions]")?.getBoundingClientRect();
+      if (r && list) {
+        const top = Math.min(r.top, list.top);
+        const left = Math.min(r.left, list.left);
+        r = new DOMRect(
+          left,
+          top,
+          Math.max(r.right, list.right) - left,
+          Math.max(r.bottom, list.bottom) - top
+        );
+      }
       const d = el?.closest("[role=dialog]")?.getBoundingClientRect() ?? null;
       setBox((prev) => (prev && d && prev.right === d.right ? prev : d));
       // Only when it moved: a new DOMRect every tick would re-render forever.