Fix duplicate user field in tasks migration

Remove duplicate AddField operation for tag.user field in
tasks/migrations/0002_initial.py. The migration was attempting
to add the user ForeignKey field twice, causing PostgreSQL to
fail with "column 'user_id' of relation 'tags' already exists".

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

tasks/migrations/0002_initial.py

@@ -35,11 +35,6 @@ class Migration(migrations.Migration):
             name='user',
             field=models.ForeignKey(on_delete=django.db.models.deletion.CASCADE, related_name='tasks', to=settings.AUTH_USER_MODEL),
         ),
-        migrations.AddField(
-            model_name='tag',
-            name='user',
-            field=models.ForeignKey(on_delete=django.db.models.deletion.CASCADE, related_name='tags', to=settings.AUTH_USER_MODEL),
-        ),
         migrations.AddField(
             model_name='task',
             name='group',