fix(worktrees): default to HEAD when no startPoint provided

- Use git reset --hard HEAD by default when startPoint is not provided or is HEAD
- Preserve resetting to the provided startPoint when a concrete value is supplied

packages/ui/src/stores/useMultiRunStore.ts

@@ -170,6 +170,7 @@ export const useMultiRunStore = create<MultiRunStore>()(
               const enrichedMetadata = {
                 ...worktreeMetadata,
                 createdFromBranch: startPoint ?? 'HEAD',
+                kind: 'standard' as const,
               };
 
               // Session title format: groupSlug/provider/model (or groupSlug/provider/model/index for duplicates)