docs(ai): add Prisma application best practices to Cursor rule

Author: ArthurGamby

apps/docs/content/docs/ai/tools/cursor.mdx

@@ -62,6 +62,18 @@ alwaysApply: false
 - When creating or managing Prisma Postgres databases, prefer the Prisma MCP server tools instead of guessing CLI/API steps.
 - Before changing Prisma setup, inspect `package.json`, `prisma.config.*`, `schema.prisma`, existing generated client imports, and the installed Prisma version.
 - Preserve existing Prisma Accelerate usage unless explicitly asked to migrate it.
+
+## Prisma application best practices
+
+- Validate inputs at API boundaries before calling Prisma Client.
+- Use `select` or scoped `include` to avoid over-fetching data.
+- Use transactions for multi-step writes that must succeed or fail together.
+- Handle known Prisma errors intentionally, especially constraint and validation errors.
+- Prefer integration tests against the same database provider used in production when testing Prisma behavior.
+- Mock Prisma Client only for isolated unit tests where database behavior is not under test.
+- Review generated migrations before applying them to shared or production environments.
+- Avoid exposing database-specific errors directly to end users.
+- Keep Prisma-related database access separate from unrelated business logic when it improves maintainability.
 ```
 
 For a simpler repo-wide setup, you can paste the same guidance into `AGENTS.md`.