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/minio.py

@@ -0,0 +1,41 @@
+import uuid
+from datetime import datetime, timezone
+from pathlib import PurePosixPath
+
+import boto3
+from botocore.config import Config as BotoConfig
+
+from app.config import settings
+
+
+def _get_client():
+    return boto3.client(
+        "s3",
+        endpoint_url=settings.minio.endpoint,
+        aws_access_key_id=settings.minio.access_key,
+        aws_secret_access_key=settings.minio.secret_key,
+        config=BotoConfig(signature_version="s3v4"),
+    )
+
+
+def _generate_object_key(filename: str) -> str:
+    now = datetime.now(timezone.utc)
+    date_prefix = now.strftime("%Y/%m/%d")
+    ext = PurePosixPath(filename).suffix or ".jpg"
+    return f"{date_prefix}/{uuid.uuid4().hex}{ext}"
+
+
+def upload_image(file_bytes: bytes, original_filename: str) -> str:
+    client = _get_client()
+    object_key = _generate_object_key(original_filename)
+    content_type = "image/jpeg"
+    if original_filename.lower().endswith(".png"):
+        content_type = "image/png"
+
+    client.put_object(
+        Bucket=settings.minio.bucket,
+        Key=object_key,
+        Body=file_bytes,
+        ContentType=content_type,
+    )
+    return object_key