refacto: reorganize files to easily add an API service

server/app/ports/reading_repository.py

@@ -0,0 +1,7 @@
+from abc import ABC, abstractmethod
+
+class ReadingRepository(ABC):
+    @abstractmethod
+    def insert_reading(self, device_id: str, pulse_count: int) -> None:
+        """Persiste un relevé"""
+        ...