feat: implement admin endpoint and UI for database and vector store reset

feat: initialize SQLAlchemy async database engine and session management with Neon-compatible configuration

feat: implement backend matching pipeline and update project documentation

feat: implement async SQLAlchemy database engine and session management with Neon-compatible configurations

feat: add pipeline page, session delete with Qdrant cleanup, explain worker, and final frontend polish

fix: resolve asyncpg ssl connection errors and Qdrant strict payload filtering

feat: scaffold FastAPI app with async Postgres and Qdrant connection