docs(generic): note Postgres MCP server availability for agentic contributors

Projects with a Postgres dependency typically expose an MCP server scoped
to their database(s). Call this out so agents know to verify schema and
query shapes against the real database rather than guessing.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

generic.md

@@ -182,6 +182,7 @@ Default for any app with a central data store.
 - Migrations via `sqlx-cli` or `refinery`; migration files live in `crates/<app>-data/migrations/`.
 - Schema changes are forward-only in production. Destructive migrations require a dedicated maintenance window and an explicit plan.
 - Use `sqlx` with compile-time query checking (`sqlx prepare`) and commit the generated `.sqlx/` offline query cache so CI builds don't need a live database.
+- **Agentic contributors working in a project with a Postgres dependency will usually have MCP access to a Postgres MCP server scoped to that project's database(s).** Prefer using the MCP server to inspect schema, verify query shapes against real tables, and sanity-check migrations before applying them — don't guess at column names or types when you can look them up. The scope is limited to the project's own databases; don't assume access to unrelated ones.
 
 ### Distributed database: Turso
 When the app's data model is distributed (edge replicas, per-site local copies with sync), use Turso. Auth via Turso-issued tokens stored in the per-host secret store, not in `manifest.yml`.