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>

pyproject.toml

@@ -0,0 +1,20 @@
+[project]
+name = "snapledger-backend"
+version = "0.1.0"
+description = "SnapLedger backend API server"
+requires-python = ">=3.10"
+dependencies = [
+    "fastapi>=0.115.0",
+    "uvicorn[standard]>=0.34.0",
+    "boto3>=1.35.0",
+    "psycopg[binary]>=3.2.0",
+    "python-multipart>=0.0.12",
+    "pydantic>=2.9.0",
+    "pyyaml>=6.0",
+]
+
+[project.optional-dependencies]
+dev = [
+    "pytest>=8.0",
+    "httpx>=0.27",
+]