Add opt-in automatic fixture blocks

[xvaara]

With autoFixtures: true, adding or editing SQL under migrations/fixtures/ automatically adds the changed fixtures to the pending migration. This is an experimental implementation of the fixture-state idea for feedback.

It supports both current.sql and current/, using marked blocks of ordinary --!include directives. Existing entries keep their placement, new entries go into the last block, and manual includes take precedence. Without a block, it appends one to current.sql or creates a final directory file using the project's number width (9-auto-fixtures.sql, 999999-auto-fixtures.sql, etc.).

Fixture discovery includes subdirectories and reuses the existing include compiler and pg-minify. The comparison baseline comes from committed include blocks; hashes are recomputed rather than stored separately. Nested fixtures are included through their outer fixture, and empty blocks retain their placement.

Also preserves include directives after a failed commit and prevents overlapping watch runs while retaining the queued rerun.

Validation: TypeScript build, ESLint, the full Jest suite, and additional current.sql commit/uncommit lifecycle tests. Coverage includes opt-in behavior, new-file discovery, comment-only changes, block placement, filename numbering, and rollback.