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/slm_ui.py

@@ -30,7 +30,7 @@ async def slm_detail_page(request: Request, unit_id: str, db: Session = Depends(
 
     # Get roster unit
     unit = db.query(RosterUnit).filter_by(id=unit_id).first()
-    if not unit or unit.device_type != "sound_level_meter":
+    if not unit or unit.device_type != "slm":
         raise HTTPException(status_code=404, detail="Sound level meter not found")
 
     return templates.TemplateResponse("slm_detail.html", {
@@ -46,7 +46,7 @@ async def get_slm_summary(unit_id: str, db: Session = Depends(get_db)):
 
     # Get roster unit
     unit = db.query(RosterUnit).filter_by(id=unit_id).first()
-    if not unit or unit.device_type != "sound_level_meter":
+    if not unit or unit.device_type != "slm":
         raise HTTPException(status_code=404, detail="Sound level meter not found")
 
     # Try to get live status from SLMM
@@ -61,7 +61,7 @@ async def get_slm_summary(unit_id: str, db: Session = Depends(get_db)):
 
     return {
         "unit_id": unit_id,
-        "device_type": "sound_level_meter",
+        "device_type": "slm",
         "deployed": unit.deployed,
         "model": unit.slm_model or "NL-43",
         "location": unit.address or unit.location,
@@ -89,7 +89,7 @@ async def slm_controls_partial(request: Request, unit_id: str, db: Session = Dep
     """Render SLM control panel partial."""
 
     unit = db.query(RosterUnit).filter_by(id=unit_id).first()
-    if not unit or unit.device_type != "sound_level_meter":
+    if not unit or unit.device_type != "slm":
         raise HTTPException(status_code=404, detail="Sound level meter not found")
 
     # Get current status from SLMM