feat: standardize device type for Sound Level Meters (SLM)

- Updated all instances of device_type from "sound_level_meter" to "slm" across the codebase.
- Enhanced documentation to reflect the new device type standardization.
- Added migration script to convert legacy device types in the database.
- Updated relevant API endpoints, models, and frontend templates to use the new device type.
- Ensured backward compatibility by deprecating the old device type without data loss.

backend/services/scheduler.py

@@ -207,7 +207,7 @@ class SchedulerService:
             project_id=action.project_id,
             location_id=action.location_id,
             unit_id=unit_id,
-            session_type="sound" if action.device_type == "sound_level_meter" else "vibration",
+            session_type="sound" if action.device_type == "slm" else "vibration",
             started_at=datetime.utcnow(),
             status="recording",
             session_metadata=json.dumps({"scheduled_action_id": action.id}),
@@ -272,7 +272,7 @@ class SchedulerService:
         # Build destination path
         # Example: data/Projects/{project-id}/sound/{location-name}/session-{timestamp}/
         session_timestamp = datetime.utcnow().strftime("%Y-%m-%d-%H%M")
-        location_type_dir = "sound" if action.device_type == "sound_level_meter" else "vibration"
+        location_type_dir = "sound" if action.device_type == "slm" else "vibration"
 
         destination_path = (
             f"data/Projects/{project.id}/{location_type_dir}/"