Implement Phase 1 backend: FastAPI upload API with MinIO and PostgreSQL

- Add FastAPI app with CORS and auth middleware (Bearer token)
- Add POST /api/v1/transactions/upload endpoint (multipart/form-data)
- Add MinIO storage service with date-partitioned object keys
- Add PostgreSQL database service for transaction metadata
- Add Dockerfile and docker-compose.yml for deployment
- Add config.example.yaml template

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

app/services/database.py

@@ -0,0 +1,29 @@
+import psycopg
+from psycopg.rows import dict_row
+
+from app.config import settings
+
+
+def _get_conn():
+    return psycopg.connect(settings.postgresql.dsn, row_factory=dict_row)
+
+
+def insert_transaction(
+    image_object_key: str,
+    original_filename: str | None,
+    user_note: str | None,
+) -> dict:
+    with _get_conn() as conn:
+        with conn.cursor() as cur:
+            cur.execute(
+                """
+                INSERT INTO transactions
+                    (image_object_key, original_filename, user_note, process_status)
+                VALUES (%s, %s, %s, 'PENDING')
+                RETURNING id, upload_time
+                """,
+                (image_object_key, original_filename, user_note),
+            )
+            row = cur.fetchone()
+        conn.commit()
+    return {"id": str(row["id"]), "upload_time": row["upload_time"].isoformat()}