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%

tests/integration/test_migrations.py

@@ -0,0 +1,44 @@
+from typing import cast
+
+import pytest
+from sqlalchemy import inspect
+from sqlalchemy.ext.asyncio import AsyncEngine, AsyncSession
+
+
+class TestMigrations:
+    @pytest.mark.asyncio
+    async def test_initial_migration_creates_post_table(self, db_session: AsyncSession) -> None:
+        engine = cast(AsyncEngine, db_session.bind)
+        async with engine.connect() as conn:
+            tables = await conn.run_sync(lambda sync_conn: inspect(sync_conn).get_table_names())
+        assert "posts" in tables
+
+    @pytest.mark.asyncio
+    async def test_posts_table_has_expected_columns(self, db_session: AsyncSession) -> None:
+        engine = cast(AsyncEngine, db_session.bind)
+        async with engine.connect() as conn:
+            columns = await conn.run_sync(lambda sync_conn: inspect(sync_conn).get_columns("posts"))
+        column_names = [col["name"] for col in columns]
+        expected = [
+            "id",
+            "title",
+            "content",
+            "slug",
+            "author_id",
+            "published",
+            "tags",
+            "created_at",
+            "updated_at",
+        ]
+        for col in expected:
+            assert col in column_names
+
+    @pytest.mark.asyncio
+    async def test_posts_table_has_indexes(self, db_session: AsyncSession) -> None:
+        engine = cast(AsyncEngine, db_session.bind)
+        async with engine.connect() as conn:
+            indexes = await conn.run_sync(lambda sync_conn: inspect(sync_conn).get_indexes("posts"))
+        index_names = [idx["name"] for idx in indexes]
+        assert "ix_posts_slug" in index_names
+        assert "ix_posts_author_id" in index_names
+        assert "ix_posts_published" in index_names