feat: add admin profile editing capability

Added admin endpoint and functionality for editing user profiles from the
report management interface:

Backend Changes:
- Added PUT /api/users/:id endpoint for admin-only profile editing
- Reuses existing updateUserSettings logic with slug uniqueness validation
- Protected with adminGuard and csrfProtection
- Proper audit logging for admin profile edits

Frontend Changes:
- Added adminUpdateUser() method to UserService
- Updated editProfile() in admin-reports to load profile and allow bio editing
- Uses prompt for quick bio editing (can be expanded to full form later)
- Shows success/error toasts and refreshes report list after edit

Admins can now quickly edit reported user profiles directly from the
report management interface.

apps/frontend/src/app/services/user.service.ts

@@ -85,4 +85,8 @@ export class UserService {
   makeProfilePrivate(userId: string): Observable<User> {
     return this.api.post<User>(`/users/${userId}/make-private`, {});
   }
+
+  adminUpdateUser(userId: string, settings: UpdateUserSettingsRequest): Observable<User> {
+    return this.api.put<User>(`/users/${userId}`, settings);
+  }
 }