Integrate embed infrastructure into the complete message flow:
- messages.ts: batch-fetch embeds in GET, resolve on POST, re-resolve on PATCH
- dm.ts: same pattern for DM messages with isDm=true
- search.ts: include embeds in all 4 search/around endpoints
- events.ts: embed resolution in WS message create/edit for both space and DM
- Fix embedClassifier.ts type errors (regex match undefined → null)
- Add embeds: [] to all inline MessageWithUser/DmMessageWithUser constructions
- Add embeds: [] to chatStore optimistic message