Feat/default notification channels

[the-last-php-bender]

Describe your changes

Briefly describe the changes you made and their purpose.

This PR implements the ability to bulk-assign Notification Channels to Alerts as requested in issue #3601. The implementation includes:

1. Default Channel: Added the ability to mark a notification channel as 'Default' so it is automatically attached to any new monitor created.
2. Bulk Edit Mode: Added checkbox selection on the Uptime and Infrastructure monitor lists to "Add Notification Channel" or "Remove Notification Channel" to all selected items.
3. Global Defaults (Apply to All): Added an "Apply to All" button in the notification edit form that applies the notification channel to all existing monitors in the team.

Backend changes:

• Added isDefault field to Notification model
• Added API endpoints: GET /notifications/defaults, PATCH /notifications/:id/default, POST /notifications/:id/apply-to-all
• Added PATCH /monitors/notifications endpoint for bulk add/remove operations
  Frontend changes:
• Added "Default channel" toggle in notification creation/edit form
• Added bulk notification actions (Add/Remove) in Uptime and Infrastructure monitor pages
• Added "Apply to All" button in notification edit form
• Auto-attaches default notifications to new monitors

Write your issue number after "Fixes "

Fixes #3601

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const { t } = useTranslation();
<div>{t('add')}</div>

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