✨(backend) add property to check if recording file is saved

Introduce new property that verifies if a recording file has a saved
status. While the implementation is straightforward, it improves code
readability and provides a clear, semantic way to check file status.

src/backend/core/models.py

@@ -578,6 +578,11 @@ class Recording(BaseModel):
             RecordingStatusChoices.STOPPED,
         }
 
+    @property
+    def is_saved(self) -> bool:
+        """Check if the recording is in a saved state."""
+        return self.status == RecordingStatusChoices.SAVED
+
     @property
     def extension(self):
         """Get recording extension based on its mode."""