This PR implements app search feature and addresses the issue #1182.
    
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## Summary by cubic
Adds a fast app search with a command-style dialog so users can find
apps by name or chat content and jump to them quickly. Implements the
search experience requested in #1182.

- New Features
- Search dialog (Ctrl+K or “Search Apps” button) with result snippets
from matching chat titles/messages.
- Searches across app names, chat titles, and message content;
case-insensitive; supports partial matches; empty query lists all apps.
  - Selecting a result navigates to the app and closes the dialog.
- New IPC endpoint search-app with Zod-validated results, debounced
React Query hook, and preload allowlist update.
- Added E2E tests for dialog open/close, shortcuts, matching behavior,
empty state, and navigation.

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