feat: M2 database migration runner with Phinx and initial schema

CONTRIBUTING.md

@@ -30,8 +30,8 @@ composer test
 ```
 
 Commit both `composer.lock` and `package-lock.json` for reproducible builds.
-`migrate` and `seed` are unavailable until M2 (#12); they exit nonzero and leave
-#10 open. Never remove volumes with `down -v`; the wrapper forbids it.
+`migrate` and `seed` are available via `./dev.sh` (M2 #12). Never remove volumes
+with `down -v`; the wrapper forbids it.
 
 `composer lint` enforces PSR-12 on PHP in `src`, `public`, `config`, `bin`,
 `templates`, `db/migrations` and `tests`. `composer test` runs foundation checks