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_repositories.py

@@ -0,0 +1,139 @@
+from uuid import uuid4
+
+import pytest
+from sqlalchemy.ext.asyncio import AsyncSession
+
+from app.domain.entities import Post
+from app.domain.value_objects import Title
+from app.infrastructure.repositories.post import SQLAlchemyPostRepository
+
+
+class TestSQLAlchemyPostRepository:
+    @pytest.fixture
+    async def repo(self, db_session: AsyncSession) -> SQLAlchemyPostRepository:
+        return SQLAlchemyPostRepository(db_session)
+
+    @pytest.mark.asyncio
+    async def test_add_creates_post(
+        self, repo: SQLAlchemyPostRepository, db_session: AsyncSession
+    ) -> None:
+        post = Post.create(
+            title_str="Test Title",
+            content_str="Test content with enough characters",
+            author_id="user-1",
+            tags=["test"],
+        )
+        await repo.add(post)
+        await db_session.commit()
+
+        result = await repo.get_by_id(post.id)
+        assert result is not None
+        assert result.title.value == "Test Title"
+        assert result.slug.value == "test-title"
+
+    @pytest.mark.asyncio
+    async def test_get_by_id_returns_post(
+        self, repo: SQLAlchemyPostRepository, db_session: AsyncSession
+    ) -> None:
+        post = Post.create(
+            title_str="Find Me",
+            content_str="Content with enough characters for validation",
+            author_id="user-1",
+        )
+        await repo.add(post)
+        await db_session.commit()
+
+        result = await repo.get_by_id(post.id)
+        assert result is not None
+        assert result.id == post.id
+
+    @pytest.mark.asyncio
+    async def test_get_by_id_returns_none_for_missing(self, repo: SQLAlchemyPostRepository) -> None:
+        result = await repo.get_by_id(uuid4())
+        assert result is None
+
+    @pytest.mark.asyncio
+    async def test_get_by_slug_returns_post(
+        self, repo: SQLAlchemyPostRepository, db_session: AsyncSession
+    ) -> None:
+        post = Post.create(
+            title_str="Slug Test",
+            content_str="Content with enough characters for validation",
+            author_id="user-1",
+        )
+        await repo.add(post)
+        await db_session.commit()
+
+        result = await repo.get_by_slug(post.slug.value)
+        assert result is not None
+        assert result.id == post.id
+
+    @pytest.mark.asyncio
+    async def test_list_with_pagination(
+        self, repo: SQLAlchemyPostRepository, db_session: AsyncSession
+    ) -> None:
+        for i in range(5):
+            post = Post.create(
+                title_str=f"Post {i}",
+                content_str="Content with enough characters for validation",
+                author_id="user-1",
+            )
+            await repo.add(post)
+        await db_session.commit()
+
+        result = await repo.get_published(limit=3, offset=0)
+        assert len(result) == 0
+
+    @pytest.mark.asyncio
+    async def test_update_modifies_post(
+        self, repo: SQLAlchemyPostRepository, db_session: AsyncSession
+    ) -> None:
+        post = Post.create(
+            title_str="Original",
+            content_str="Content with enough characters for validation",
+            author_id="user-1",
+        )
+        await repo.add(post)
+        await db_session.commit()
+
+        post.update_title(Title("Updated"))
+        await repo.update(post)
+        await db_session.commit()
+
+        result = await repo.get_by_id(post.id)
+        assert result is not None
+        assert result.title.value == "Updated"
+        assert result.slug.value == "updated"
+
+    @pytest.mark.asyncio
+    async def test_delete_removes_post(
+        self, repo: SQLAlchemyPostRepository, db_session: AsyncSession
+    ) -> None:
+        post = Post.create(
+            title_str="To Delete",
+            content_str="Content with enough characters for validation",
+            author_id="user-1",
+        )
+        await repo.add(post)
+        await db_session.commit()
+
+        await repo.delete(post.id)
+        await db_session.commit()
+
+        result = await repo.get_by_id(post.id)
+        assert result is None
+
+    @pytest.mark.asyncio
+    async def test_slug_exists_checks_uniqueness(
+        self, repo: SQLAlchemyPostRepository, db_session: AsyncSession
+    ) -> None:
+        post = Post.create(
+            title_str="Unique Slug",
+            content_str="Content with enough characters for validation",
+            author_id="user-1",
+        )
+        await repo.add(post)
+        await db_session.commit()
+
+        assert await repo.slug_exists(post.slug.value) is True
+        assert await repo.slug_exists("nonexistent-slug") is False