docs(m3): place create decisions in the contracts

- DATA-MODEL.md: storage engine (stdlib sqlite3 + schema.sql, no ORM/migrations),
  pragmas, per-test isolation.
- API.md: revision coupling, async job model, PUT check order, server-derived ready.
- PROMPTS.md: no prompt files ship; the DB is the only prompt source.

docs/contracts/PROMPTS.md

@@ -19,7 +19,8 @@ Owns prompt storage, prompt inputs, and the two inference calls.
 ## 1. Storage and revisions
 
 - Prompts live in the database, not in text files, with all revisions retained. Tables are in
-  `docs/contracts/DATA-MODEL.md` §7.
+  `docs/contracts/DATA-MODEL.md` §7. No prompt files ship with the application; the database is
+  the only prompt source.
 - Each call reads the active revision fresh.
 - Editing a prompt creates a new revision; history is never overwritten.
 - Every generation is logged with its inputs, the request/response when a model was used, and the