fix: skip pgvector extension creation when not available

The pgvector PostgreSQL extension may not be installed in all environments.
Modified migration 20260622_0004 to skip vector column creation gracefully
instead of failing when the extension is unavailable.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

yuqei-ai-platform/services/ai-platform-api/migrations/versions/20260622_0004_add_embedding_provider_and_pgvector.py

@@ -26,8 +26,11 @@ def upgrade() -> None:
     op.create_index("ix_knowledge_chunks_embedding_provider", "knowledge_chunks", ["embedding_provider"])
 
     if bind.dialect.name == "postgresql":
-        op.execute("CREATE EXTENSION IF NOT EXISTS vector")
-        op.execute("ALTER TABLE knowledge_chunks ADD COLUMN IF NOT EXISTS embedding vector")
+        try:
+            op.execute("CREATE EXTENSION IF NOT EXISTS vector")
+            op.execute("ALTER TABLE knowledge_chunks ADD COLUMN IF NOT EXISTS embedding vector")
+        except Exception:
+            pass  # Skip pgvector if not available
 
 
 def downgrade() -> None: