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

Extracts cache, execution, and invalidation logic into dedicated utility modules:
- query-cache.ts: Cache state management, snapshot memoization, ref counting, generation tracking
- query-executor.ts: Query execution with deduplication, retry logic, error handling
- query-invalidation.ts: Cache invalidation strategies, data access

The hook is reduced to orchestration only (~270 lines, -44% from original).

Bug fixes included:
- Fixed infinite retry loop via isEnabled callback
- Fixed memory leak with proper cleanup of GC timeouts, retry state, and in-flight promises

Comprehensive unit tests added:
- query-cache.test.ts: 57 tests for cache operations
- query-executor.test.ts: 23 tests for execution and retry logic
- query-invalidation.test.ts: 29 tests for invalidation operations
- Total: 109 new tests

Author: brandonkachen