refactor(cli): simplify use-activity-query.ts (Commit 2.6)

📊 ~810 implementation lines, ~1,630 test lines

Extracts query infrastructure from use-activity-query.ts into focused modules:
- query-cache.ts: LRU cache with generation tracking to prevent stale updates
- query-executor.ts: Debounced query execution with cancellation
- query-invalidation.ts: Cache invalidation utilities

Includes comprehensive unit tests (100+ tests) covering:
- Cache operations (get, set, delete, TTL)
- Generation tracking to prevent cache resurrection
- Query deduplication and debouncing
- Invalidation patterns

Author: brandonkachen