fix(announcements): wire announcements slice into mergeWireSnapshot

The per-slice wire-merge introduced in #77 (d1aa7b9) enumerates every
AppState slice; the announcements slice that landed on this branch
needs the same merge line so the AppState object literal still
satisfies the type. TypeScript catches this by design — that's the
guard the new helper documents.

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

Author: frenchie4111

src/shared/state/index.ts

@@ -316,7 +316,8 @@ export function mergeWireSnapshot(state: WireSnapshotState): AppState {
     costs: { ...initialState.costs, ...state.costs },
     browser: { ...initialState.browser, ...state.browser },
     jsonClaude: { ...initialState.jsonClaude, ...state.jsonClaude },
-    snooze: { ...initialState.snooze, ...state.snooze }
+    snooze: { ...initialState.snooze, ...state.snooze },
+    announcements: { ...initialState.announcements, ...state.announcements }
   }
 }