Add Chinese documentation for custom skills development and reference guide

- Created a new document for custom skills development (`custom.md`) detailing the structure, creation, implementation, and best practices for developing custom CCW skills.
- Added an index document (`index.md`) summarizing all built-in skills, their categories, and usage examples.
- Introduced a reference guide (`reference.md`) providing a quick reference for all 33 built-in CCW skills, including triggers and purposes.

ccw/frontend/src/locales/en/review-session.json

@@ -96,6 +96,11 @@
     "message": "Try adjusting your filters or search query.",
     "noFixProgress": "No fix progress data available"
   },
+  "notExecuted": {
+    "title": "Review Not Yet Executed",
+    "message": "This review session has been created but the review process has not been started yet. No findings have been generated.",
+    "hint": "💡 Tip: Execute the review workflow to start analyzing code and generate findings."
+  },
   "notFound": {
     "title": "Review Session Not Found",
     "message": "The requested review session could not be found."