Kill design-only mock surfaces + wire real offline indicator

P1 — cut showcases:
- Delete gallery.tsx (Primitives) and StatesScreen/Specimen from states.tsx
  (keep the reusable EmptyState/OfflineBanner/ModelAwayState).
- Delete placeholder-screen.tsx ('built in a later phase' stub).
- app-shell: drop the states/primitives views, the dev-rail block, the
  PHASE/TITLE maps, the INBOX_UNREAD=3 fixture fallback, and the now-dead demo state.

P2 — real connectivity:
- Replace the fake 'toggle the connection (demo)' button with a live status dot
  derived from the reconcile: green online, red when serving the stale cache
  (gitea unreachable), amber while connecting. OfflineBanner + chat offline now
  reflect real state, not a manual toggle.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

apps/desktop/src/preload/index.ts

@@ -27,6 +27,8 @@ const api = {
   config: {
     /** The saved config (never the token) — null when unset. */
     get: () => ipcRenderer.invoke('config:get'),
+    /** Discover the owners + repos a token can reach (for the onboarding pickers). */
+    discover: (conn: unknown) => ipcRenderer.invoke('config:discover', conn),
     /** Validate a token + repo before saving. */
     test: (cfg: unknown) => ipcRenderer.invoke('config:test', cfg),
     /** Save config (token encrypted in main); takes effect without restart. */