feat: add migration framework with FastMigrate integration

- Add migrations.py with create_migration, run_migrations, get_db_version
- Implement CLI migrate and create-migration commands
- Use FastMigrate's sequential 0001-*.sql naming convention
- Add comprehensive unit, integration, and E2E tests (35 tests)
- Add fresh_db_path and temp_migrations_dir test fixtures

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

tests/conftest.py

@@ -7,6 +7,33 @@ import tempfile
 import pytest
 
 
+@pytest.fixture
+def temp_migrations_dir(tmp_path):
+    """Create a temporary migrations directory for testing."""
+    migrations_path = tmp_path / "migrations"
+    migrations_path.mkdir()
+    return migrations_path
+
+
+@pytest.fixture
+def fresh_db_path(tmp_path):
+    """Provide a path for a non-existent database file.
+
+    Unlike temp_db_path, this does not create the file - it just provides
+    a path. This is needed for fastmigrate which expects to create the db.
+    """
+    db_path = tmp_path / "test.db"
+    yield db_path
+    # Cleanup
+    if db_path.exists():
+        db_path.unlink()
+    # Also clean up WAL files if they exist
+    for suffix in ["-shm", "-wal", "-journal"]:
+        wal_path = db_path.with_suffix(db_path.suffix + suffix)
+        if wal_path.exists():
+            wal_path.unlink()
+
+
 @pytest.fixture
 def temp_db_path():
     """Create a temporary database file path for testing."""