fix(cursor): fallback when requested model is unavailable

- resolve request model against current available catalog

- choose safe default when configured default id is not present

- add tests and docs for daemon request-model fallback behavior

docs/cursor-integration.md

@@ -60,6 +60,7 @@ ccs cursor stop
 - `ghost_mode`: enabled
 - `auto_start`: disabled
 - Model list resolution: authenticated live fetch when available, with cached/default fallback.
+- Request model validation: if a requested model is not present in the available Cursor model catalog, daemon falls back to the resolved default model.
 
 These values are managed in unified config and can be updated from CLI or dashboard.