MAESTRO: add base scanner protocol

backend/app/engine/scanner_base.py

@@ -0,0 +1,14 @@
+from __future__ import annotations
+
+from typing import Protocol
+
+from .models import TestResult
+from .parser import ParsedHeader
+
+
+class BaseScanner(Protocol):
+    id: int
+    name: str
+
+    def run(self, headers: list[ParsedHeader]) -> TestResult | None:
+        """Run the scanner against parsed headers."""