* fix(group): surface friendly error when group name not found
Squashed commits:
- test(csharp): add #903 regression — parse completeness for single-file C# repo
- fix(group): add GroupNotFoundError guard to groupList + re-throw tests for groupQuery/groupStatus
- fix(test): restore section comments in csharp.test.ts stripped during rebase
* fix(group): catch GroupNotFoundError explicitly in groupContext and groupImpact