* Implement migration safety rules:
- MIG001: Warn on CREATE INDEX without CONCURRENT.
- MIG002: Warn on ALTER TABLE ADD COLUMN NOT NULL without DEFAULT.
- MIG003: Warn on ALTER TABLE ADD CONSTRAINT without NOT VALID.
* Implement naming conventions rules:
- NAM001: Warn on non-snake_case table names.
- NAM002: Warn on non-snake_case column names in CREATE TABLE.
- NAM003: Warn on non-snake_case function names.
* Add test fixtures for all new rules.
