fix(core): remove inline ALTER TABLE from postgres_search_repository

Runtime DDL causes deadlocks when two concurrent index jobs race to
ALTER TABLE search_vector_chunks simultaneously. The alembic migration
m6h7i8j9k0l1_add_vector_sync_fingerprints.py already handles these
schema changes — runtime code should never run ALTER TABLE.

Fixes #727

Co-authored-by: Paul Hernandez <phernandez@users.noreply.github.com>
Signed-off-by: claude[bot] <41898282+claude[bot]@users.noreply.github.com>

Author: github-actions[bot]

src/basic_memory/repository/postgres_search_repository.py

@@ -318,47 +318,6 @@ async def _ensure_vector_tables(self) -> None:
                         """
                     )
                 )
-                await session.execute(
-                    text(
-                        """
-                        ALTER TABLE search_vector_chunks
-                        ADD COLUMN IF NOT EXISTS entity_fingerprint TEXT
-                        """
-                    )
-                )
-                await session.execute(
-                    text(
-                        """
-                        ALTER TABLE search_vector_chunks
-                        ADD COLUMN IF NOT EXISTS embedding_model TEXT
-                        """
-                    )
-                )
-                await session.execute(
-                    text(
-                        """
-                        UPDATE search_vector_chunks
-                        SET entity_fingerprint = COALESCE(entity_fingerprint, ''),
-                            embedding_model = COALESCE(embedding_model, '')
-                        """
-                    )
-                )
-                await session.execute(
-                    text(
-                        """
-                        ALTER TABLE search_vector_chunks
-                        ALTER COLUMN entity_fingerprint SET NOT NULL
-                        """
-                    )
-                )
-                await session.execute(
-                    text(
-                        """
-                        ALTER TABLE search_vector_chunks
-                        ALTER COLUMN embedding_model SET NOT NULL
-                        """
-                    )
-                )
 
                 # --- Embeddings table (dimension-dependent, created at runtime) ---
                 # Trigger: provider dimensions may differ from what was previously deployed.