Project folders for the agent, Local, the menu under its button

- Settings… lists the folders the agent may work in, with the system's
  folder dialog, remove, max mode and terminal, all through
  'lembas remote … --json' (CLI 1.2.0). Turning the agent on with no
  folder opens it; the title bar says 'agent: no folders' instead of green.
- The content webview's User-Agent carries LLeMbasDesktop/<v> (host=…),
  so the server can show this computer's device as Local.
- The title bar menu pops up at the button (popup_menu_at): Wayland gave
  the pointer-less popup the middle of the window.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

ui/tokens.css

@@ -13,7 +13,7 @@
   --radius: 2px;
   --press: 2px;
   --control-h: 2.5rem;
-  --card-max: 34rem;
+  --card-max: 40rem;
 
   color-scheme: dark;
   --bg: #0B0D10;