fix(qoder): allow qmodel_latest model key

- Add qmodel_latest to QODER_MODEL_MAP
- Expose qmodel_latest in static Qoder provider catalog (qd)
- Generalize executor comment so model set does not go stale
- Add unit coverage for the new model key + catalog

Closes #1638

Co-authored-by: Cursor <cursoragent@cursor.com>

src/lib/qoder/constants.js

@@ -46,6 +46,7 @@ export const QODER_MODEL_MAP = {
   lite: "lite",
   // Frontier models
   qmodel: "qmodel",
+  qmodel_latest: "qmodel_latest",
   dmodel: "dmodel",
   dfmodel: "dfmodel",
   gm51model: "gm51model",