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/config.py

@@ -0,0 +1,48 @@
+from pathlib import Path
+
+import yaml
+from pydantic import BaseModel
+
+
+class MinioConfig(BaseModel):
+    endpoint: str
+    bucket: str = "snapledger"
+    access_key: str
+    secret_key: str
+
+
+class PostgresConfig(BaseModel):
+    host: str
+    port: int = 5432
+    database: str = "snapledger"
+    user: str
+    password: str
+
+    @property
+    def dsn(self) -> str:
+        return (
+            f"postgresql://{self.user}:{self.password}"
+            f"@{self.host}:{self.port}/{self.database}"
+        )
+
+
+class ApiConfig(BaseModel):
+    token: str
+
+
+class AppConfig(BaseModel):
+    minio: MinioConfig
+    postgresql: PostgresConfig
+    api: ApiConfig
+
+
+def load_config(path: str = "config.yaml") -> AppConfig:
+    config_path = Path(path)
+    if not config_path.exists():
+        raise FileNotFoundError(f"Configuration file not found: {path}")
+    with open(config_path, encoding="utf-8") as f:
+        data = yaml.safe_load(f)
+    return AppConfig(**data)
+
+
+settings = load_config()