fix: incluir group_id en SELECT de unassignTask y simplificar condición

Co-authored-by: aider (openrouter/openai/gpt-5) <aider@aider.chat>

src/tasks/service.ts

@@ -483,7 +483,7 @@ export class TaskService {
 
     const existing = this.dbInstance
       .prepare(`
-        SELECT id, description, due_date, completed, completed_at, display_code
+        SELECT id, description, due_date, group_id, completed, completed_at, display_code
         FROM tasks
         WHERE id = ?
       `)
@@ -515,7 +515,7 @@ export class TaskService {
       `).get(ensuredUser, taskId) as any;
       const cnt = Number(stats?.cnt || 0);
       const mine = Number(stats?.mine || 0) > 0;
-      if ((existing.group_id == null || existing.group_id === null) && cnt === 1 && mine) {
+      if (existing.group_id == null && cnt === 1 && mine) {
         return {
           status: 'forbidden_personal',
           task: {