feat(ui): enhance doctor and error manager with new ui layer

- doctor.ts: add styled header box, semantic status indicators,
  formatted summary table, grouped check sections
- error-manager.ts: add boxed error messages, styled solution
  sections, semantic color coding for all error types
- ccs.ts, shell-executor.ts: await async error methods

Phase 4 of CLI UI Enhancement plan complete.

src/utils/shell-executor.ts

@@ -52,8 +52,8 @@ export function execClaude(
     else process.exit(code || 0);
   });
 
-  child.on('error', () => {
-    ErrorManager.showClaudeNotFound();
+  child.on('error', async () => {
+    await ErrorManager.showClaudeNotFound();
     process.exit(1);
   });
 }