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/routers/project_locations.py

@@ -273,7 +273,7 @@ async def assign_unit_to_location(
         raise HTTPException(status_code=404, detail="Unit not found")
 
     # Check device type matches location type
-    expected_device_type = "sound_level_meter" if location.location_type == "sound" else "seismograph"
+    expected_device_type = "slm" if location.location_type == "sound" else "seismograph"
     if unit.device_type != expected_device_type:
         raise HTTPException(
             status_code=400,
@@ -375,7 +375,7 @@ async def get_available_units(
     Filters by device type matching the location type.
     """
     # Determine required device type
-    required_device_type = "sound_level_meter" if location_type == "sound" else "seismograph"
+    required_device_type = "slm" if location_type == "sound" else "seismograph"
 
     # Get all units of the required type that are deployed and not retired
     all_units = db.query(RosterUnit).filter(
@@ -397,7 +397,7 @@ async def get_available_units(
             "id": unit.id,
             "device_type": unit.device_type,
             "location": unit.address or unit.location,
-            "model": unit.slm_model if unit.device_type == "sound_level_meter" else unit.unit_type,
+            "model": unit.slm_model if unit.device_type == "slm" else unit.unit_type,
         }
         for unit in all_units
         if unit.id not in assigned_unit_ids