[codex] Improve query cache refresh behavior

[philcunliffe]

Summary

• make proxy_messages cache refresh incremental for same-day JSONL growth, with bounded replay for stream reconstruction and prior-seen lookups streamed from Iceberg
• switch query execution for cache-backed datasets and collections to Iceberg data sources so scans can project only requested/scope columns instead of reading full tables up front
• soften stale-cache messaging to report when the cache was last refreshed, and update CLI tests, README, and bundled query-skill docs

Why

The query cache path was doing too much full-file/full-table work for growing proxy recordings, and the stale-cache warning phrasing was too easy for LLM callers to misinterpret as a hard data-quality failure. This keeps the freshness behavior while making the CLI message factual and timestamp-oriented.

Validation

• npm test
• npm run typecheck
• npm run lint (exits 0; existing warnings remain)
• git diff --check