Add task caching with delta sync

[krisrowe]

Problem

Every list_tasks call fetches all tasks from the API, which is inefficient for:

• Large projects with many tasks
• Frequent polling/checks
• Rate limit concerns

Proposed Solution

Implement local caching with delta synchronization:

1. Cache tasks locally after initial fetch
2. On subsequent calls, only fetch changes since last sync
3. Merge deltas into local cache
4. Return from cache for read operations

This would improve performance and reduce API calls significantly.