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/routers/upload.py

@@ -0,0 +1,61 @@
+import logging
+
+from fastapi import APIRouter, File, Form, UploadFile
+from fastapi.responses import JSONResponse
+
+from app.services import database, minio
+
+router = APIRouter(tags=["upload"])
+logger = logging.getLogger(__name__)
+
+MAX_FILE_SIZE = 10 * 1024 * 1024  # 10 MB
+
+
+@router.post("/transactions/upload")
+async def upload_transaction(
+    file: UploadFile = File(...),
+    original_filename: str | None = Form(None),
+    user_note: str | None = Form(None),
+):
+    # Read file content
+    content = await file.read()
+
+    if len(content) == 0:
+        return JSONResponse(
+            status_code=422,
+            content={"success": False, "error": "Missing required field: file"},
+        )
+
+    if len(content) > MAX_FILE_SIZE:
+        return JSONResponse(
+            status_code=413,
+            content={"success": False, "error": "File size exceeds 10MB limit"},
+        )
+
+    filename = original_filename or file.filename or "upload.jpg"
+
+    # Upload to MinIO
+    try:
+        object_key = minio.upload_image(content, filename)
+    except Exception:
+        logger.exception("Failed to upload image to storage")
+        return JSONResponse(
+            status_code=503,
+            content={"success": False, "error": "Storage service unavailable"},
+        )
+
+    # Insert metadata into PostgreSQL
+    try:
+        result = database.insert_transaction(
+            image_object_key=object_key,
+            original_filename=filename,
+            user_note=user_note if user_note else None,
+        )
+    except Exception:
+        logger.exception("Failed to save transaction metadata")
+        return JSONResponse(
+            status_code=500,
+            content={"success": False, "error": "Failed to save transaction metadata"},
+        )
+
+    return {"success": True, "data": result}