fix: cap stored attachment text to avoid exceeding max_allowed_packet

[ShrihariMahabal]

Summary

Large attachments' full extracted text was stored in the attachments table, risking MySQL's max_allowed_packet. The stored column is now capped to the inline-injection threshold, while retrieval-mode chunking/embedding uses the full in-memory text instead of the (now-capped) row.

[greptile-apps]

Confidence Score: 5/5

Safe to merge — the cap is applied only to the DB write while the full text is correctly threaded through to the embedder.

The routing decision, chunking, and embedding all continue to use the complete extracted text; only the persisted column is truncated. The fallback in _index_retrieval_attachments (using row.extracted_text) is only reached if the in-memory dict lookup misses, which cannot happen on the normal call path introduced here.

No files require special attention.

_{Reviews (2): Last reviewed commit: "fix: cap stored attachment text to avoid..." | Re-trigger Greptile}