Postgres vector migration (#84)

* feat: Implement PostgreSQL with pgvector as ChromaDB alternative

- Add PostgresVectorService with full pgvector integration
- Create PostgresVectorAdapter for ChromaDB compatibility
- Update config to support vector storage type selection
- Add factory pattern for seamless backend switching
- Include migration script with data optimization
- Add comprehensive tests for PostgreSQL implementation
- Update dependencies and environment configuration
- Expected memory reduction: 300-350MB (from 400MB+ to 50-150MB)

This enables deployment on Render's 512MB free tier by using persistent
PostgreSQL storage instead of in-memory ChromaDB.

* Add pgvector init script, update migration docs, and test adjustments

* feat: Default to postgres and automate DB init

run.sh

@@ -6,6 +6,10 @@ WORKERS_VALUE="${WORKERS:-1}"
 TIMEOUT_VALUE="${TIMEOUT:-120}"
 PORT_VALUE="${PORT:-10000}"
 
+# Initialize the database
+echo "Initializing database..."
+python scripts/init_pgvector.py
+
 echo "Starting gunicorn on port ${PORT_VALUE} with ${WORKERS_VALUE} workers and timeout ${TIMEOUT_VALUE}s"
 export PYTHONPATH="/app${PYTHONPATH:+:$PYTHONPATH}"
 exec gunicorn --bind 0.0.0.0:${PORT_VALUE} --workers "${WORKERS_VALUE}" --timeout "${TIMEOUT_VALUE}" app:app

src/config.py

@@ -15,7 +15,7 @@ CORPUS_DIRECTORY = "synthetic_policies"
 
 # Vector Database Settings
 VECTOR_STORAGE_TYPE = os.getenv(
-    "VECTOR_STORAGE_TYPE", "chroma"
+    "VECTOR_STORAGE_TYPE", "postgres"
 )  # "chroma" or "postgres"
 VECTOR_DB_PERSIST_PATH = "data/chroma_db"  # Used for ChromaDB
 DATABASE_URL = os.getenv("DATABASE_URL")  # Used for PostgreSQL