Initial implementation of pgvector and Oracle 26ai vector search demo

Three FastAPI backends comparing PostgreSQL/pgvector and Oracle 26ai for
semantic image search using CLIP embeddings: Python-side embedding for both
databases, plus Oracle in-database embedding via VECTOR_EMBEDDING(CLIP_TXT).

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

pgvector-demo/backend/db.py

@@ -0,0 +1,14 @@
+import os
+import psycopg2
+from dotenv import load_dotenv
+
+load_dotenv()
+
+def get_connection():
+    return psycopg2.connect(
+        host=os.getenv("DB_HOST"),
+        port=os.getenv("DB_PORT"),
+        dbname=os.getenv("DB_NAME"),
+        user=os.getenv("DB_USER"),
+        password=os.getenv("DB_PASSWORD"),
+    )