feat: add alembic migrations, integration tests, and CI support

- Add alembic dependency and initialize migration framework
- Configure async alembic env.py for SQLAlchemy 2.0
- Create initial migration for PostORM table
- Gate init_db() with SKIP_INIT_DB env var for CI/production
- Add PostgreSQL service to Woodpecker CI pipeline
- Create integration tests for migrations (TC-INT-001..002)
- Create integration tests for SQLAlchemyPostRepository (TC-INT-003..009)
- Add unit test for init_db skip behavior (TC-UNIT-901)
- All 176 tests pass, coverage 72.59%

pyproject.toml

@@ -12,6 +12,7 @@ dependencies = [
     "sqlalchemy>=2.0.0",
     "aiosqlite>=0.21.0",
     "asyncpg>=0.30.0",
+    "alembic>=1.15.0",
     "dishka>=1.5.0",
     "httpx>=0.28.0",
     "jinja2>=3.1.6",