Fix #134: Add validation for duplicate profile names

- Add validation in create_profile() to check for existing names before insert
- Add validation in update_profile() to prevent renaming to duplicate names
- Improve error handling in API endpoints with user-friendly messages
- Add comprehensive test suite for duplicate name validation
- Update CHANGELOG.md with fix details

This fix prevents database constraint violations and provides clear
error messages when users attempt to create or update profiles with
names that already exist in the database.

backend/main.py

@@ -221,7 +221,10 @@ async def create_profile(
     """Create a new voice profile."""
     try:
         return await profiles.create_profile(data, db)
+    except ValueError as e:
+        raise HTTPException(status_code=400, detail=str(e))
     except Exception as e:
+        # Fallback for unexpected errors
         raise HTTPException(status_code=400, detail=str(e))
 
 
@@ -277,10 +280,13 @@ async def update_profile(
     db: Session = Depends(get_db),
 ):
     """Update a voice profile."""
-    profile = await profiles.update_profile(profile_id, data, db)
-    if not profile:
-        raise HTTPException(status_code=404, detail="Profile not found")
-    return profile
+    try:
+        profile = await profiles.update_profile(profile_id, data, db)
+        if not profile:
+            raise HTTPException(status_code=404, detail="Profile not found")
+        return profile
+    except ValueError as e:
+        raise HTTPException(status_code=400, detail=str(e))
 
 
 @app.delete("/profiles/{profile_id}")