Add full notification preferences system

Users can now control which in-app and email notifications they receive
from their Settings tab on their channel page.

Bell (in-app) preferences:
- New comment on my video (default: on)
- Reply to my comment (default: on)
- Comment liked (default: on)
- Video liked (default: on)
- New subscriber (default: on)
- New video from channels I follow (default: on)
- New post from channels I follow (default: on)
- New user registration — super admins only (default: on)

Email preferences (same set plus):
- Comment liked (default: off — too noisy)
- Video liked (default: off — too noisy)
- New post from channels I follow (default: off)
- My video finished processing (default: on)
- Weekly activity digest every Monday (default: on)
- New user registration — super admins only (default: on)

Implementation:
- Migration: notification_preferences JSON column on users table
- User::notificationPref($key) helper with typed defaults
- All existing notification classes updated to check prefs in via()
- 4 new notification classes: NewSubscriberNotification,
  VideoLikedNotification, NewPostNotification, WeeklyDigestNotification
- 8 new email views matching existing dark theme
- SendWeeklyDigest artisan command, scheduled every Monday 09:00
- NewSubscriberNotification wired into UserController::toggleSubscribe
- VideoLikedNotification wired into UserController::toggleLike
- NewPostNotification wired into PostController::store (to all subscribers)
- Bell renderer updated for new_subscriber, video_like, new_post types
- Preferences saved via AJAX (POST /settings/notifications) — instant
  toggle with automatic revert on failure

Co-Authored-By: Claude Sonnet 4.6 <[email protected]>

routes/web.php

@@ -95,6 +95,7 @@ Route::middleware(['auth', 'verified'])->group(function () {
     // Settings
     Route::get('/settings', [UserController::class, 'settings'])->name('settings');
     Route::put('/settings', [UserController::class, 'updateSettings'])->name('settings.update');
+    Route::post('/settings/notifications', [UserController::class, 'updateNotificationPreferences'])->name('settings.notifications');
 
     // History & Liked
     Route::get('/history', [UserController::class, 'history'])->name('history');