- Add searchMessages method to AppDatabase with LIKE query, wildcard escaping, channel scoping, ORDER BY created_at DESC with limit
- Add searchMessages IPC channel and searchMessagesSchema to contracts.ts
- Register IPC handler in ipc-agent-coordination-handlers.ts with Zod validation
- Wire searchMessages through preload bridge
- Add 8 unit tests covering body/subject search, wildcard escaping, channel scoping, empty results, limit, and ordering
