Handle DELETE /user/scene/{id} so app routine deletion persists

[Ahmed-max]

Handle DELETE /user/scene/{id}

Deleting a routine in the Roborock app didn't persist. The app sends DELETE /user/scene/{id}, but no rule matched it, so the request fell through to the catchall. The catchall returned {"ok": true} without changing the inventory, so the routine came back on the next refresh.

Changes

• Add delete_scene in routes/user/scene/service.py. It removes the scene from scenes, home_scenes and scene_order.
• Add a DELETE-only matcher and builder in routes/user/scene/item.py, and register the delete_scene rule in endpoint_rules.py.
• Deleting an unknown id returns success, so repeated deletes are safe.

Testing

• Added tests/test_scene_delete.py; uv run pytest -q passes.
• Verified with the Roborock Android app on the HA add-on: deleted routines stay deleted.

[Lash-L]

TY @Ahmed-max!