feat(chat): slash-command autocomplete

Typing / opens a command panel from the guild's synced OpenClaw catalog
(GET /api/commands): filter + ↑↓/Enter/Esc; pick inserts /<nativeName> ;
arg stage lists args (required/type/desc) with clickable choice chips
(dynamic choices already snapshotted server-side). Sent as a normal
message — execution flows plugin -> OpenClaw command system.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

README.md

@@ -25,6 +25,9 @@ UI; it is served on the web and **bundled unchanged** into `Fabric.Desktop`
   iframe / plain text), live via `canvas.*` sockets; sharer-only edit/remove.
 - **Right-click menus** — native menu overridden with resource-specific
   context menus (guild / channel / message / user / blank areas).
+- **Slash autocomplete** — typing `/` opens a command panel from the
+  guild's synced OpenClaw catalog (`GET /api/commands`): filter, ↑↓/Enter/
+  Esc, pick inserts `/<name> `, arg stage shows args + clickable choices.
 - **Dev mode** — surfaces guild `/ack` and per-message `wakeup` metadata
   (off by default; persisted in `localStorage`).
 - Routing is `BrowserRouter` on the web and `HashRouter` under `file://`