#650 release: test → main — /api/chat cutover (#645/#632), SongStats (#635), exclude empty chats (#633), credit digest (#634)

Promotes test to main (9 commits).

Headline:

• BREAKING — POST /api/chat/workflow → POST /api/chat (#645); legacy /api/chat streaming endpoint removed (#632).
• Research provider migrated to SongStats (#635).
• GET /api/chats excludes zero-message chats (#633).
• Credit-spend visibility digest cron (#634).

🤖 Generated with Claude Code

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Summary by cubic

Cut over chat to POST /api/chat (breaking), migrated research to SongStats, and added a credit-spend digest. GET /api/chats now hides chats with no messages.

• New Features

  • Research now powered by SongStats; removed Chartmetric and unused research routes; slow paths use up to 60s.
  • Credit-spend visibility digest via Vercel Cron (*/10) hits GET /api/internal/credit-spend-digest; posts per-account summary to Telegram; guarded by CRON_SECRET.
  • Chats listing excludes zero-message chats via chat_messages!inner join.

• Migration

  • Breaking: rename POST /api/chat/workflow to POST /api/chat. Update all clients.
  • Legacy /api/chat streaming endpoint removed.