feat: Query result caching layer

[hfmsio]

Summary

Add caching for query results to improve performance for repeated queries.

Use Cases

• Re-running same query without re-fetching remote data
• Caching expensive aggregations
• Offline access to previous results

Proposed Implementation

• Hash-based cache key (query + parameters)
• IndexedDB for persistent storage
• Configurable TTL per query/connector
• Cache invalidation on schema changes
• Memory limits with LRU eviction

Considerations

• Cache size limits (browser storage quotas)
• Freshness vs performance tradeoffs
• Per-connector cache strategies (remote URLs vs local files)

Labels

enhancement, performance