Add integration tests for migration categories and execution

- Implemented MigrationCategoryTests to validate migration categorization for startup, release, seed, and data migrations.
- Added tests for edge cases, including null, empty, and whitespace migration names.
- Created StartupMigrationHostTests to verify the behavior of the migration host with real PostgreSQL instances using Testcontainers.
- Included tests for migration execution, schema creation, and handling of pending release migrations.
- Added SQL migration files for testing: creating a test table, adding a column, a release migration, and seeding data.

docs/implplan/SPRINT_506_ops_devops_iv.md

@@ -16,6 +16,8 @@
 - docs/modules/devops/architecture.md
 - ops/devops/README.md
 
+> **BLOCKED Tasks:** Before working on BLOCKED tasks, review [BLOCKED_DEPENDENCY_TREE.md](./BLOCKED_DEPENDENCY_TREE.md) for root blockers and dependencies.
+
 ## Delivery Tracker
 | # | Task ID | Status | Key dependency / next step | Owners | Task Definition |
 | --- | --- | --- | --- | --- | --- |