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/auth.py

@@ -0,0 +1,33 @@
+from fastapi import Request
+from fastapi.responses import JSONResponse
+from starlette.middleware.base import BaseHTTPMiddleware
+
+from app.config import settings
+
+
+class AuthMiddleware(BaseHTTPMiddleware):
+    async def dispatch(self, request: Request, call_next):
+        if not request.url.path.startswith("/api/v1"):
+            return await call_next(request)
+
+        token = settings.api.token
+        if not token:
+            return JSONResponse(
+                status_code=500,
+                content={"success": False, "error": "Server configuration error"},
+            )
+
+        auth_header = request.headers.get("Authorization")
+        if not auth_header or not auth_header.startswith("Bearer "):
+            return JSONResponse(
+                status_code=401,
+                content={"success": False, "error": "Missing authentication token"},
+            )
+
+        if auth_header.removeprefix("Bearer ") != token:
+            return JSONResponse(
+                status_code=403,
+                content={"success": False, "error": "Invalid authentication token"},
+            )
+
+        return await call_next(request)