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]>

resources/views/emails/comment-liked.blade.php

@@ -0,0 +1,27 @@
+<x-emails.layout subject="{{ $liker->name }} liked your comment">
+
+    <div style="width:64px;height:64px;border-radius:50%;background:rgba(230,30,30,.12);border:1px solid rgba(230,30,30,.25);margin:0 auto 24px;text-align:center;line-height:64px;font-size:28px;">&#x1F44D;</div>
+
+    <h1 class="email-title">Your comment got a like!</h1>
+    <p class="email-subtitle">On the video <strong style="color:#f1f1f1;">{{ $video->title }}</strong>.</p>
+
+    <p class="email-text">Hi <strong style="color:#f1f1f1;">{{ $recipient->name }}</strong>,</p>
+    <p class="email-text">
+        <strong style="color:#f1f1f1;">{{ $liker->name }}</strong> liked your comment:
+    </p>
+
+    <div class="email-infobox">
+        <div class="email-infobox-label">Your Comment</div>
+        <div style="color:#e0e0e0;font-size:14px;line-height:1.6;padding:4px 0;">
+            "{{ \Illuminate\Support\Str::limit(strip_tags($comment->body), 200) }}"
+        </div>
+    </div>
+
+    <div class="email-btn-wrap">
+        <a href="{{ route('videos.show', $video) }}" class="email-btn">&#x25B6;&nbsp; View Video</a>
+    </div>
+
+    <hr class="email-divider">
+    <p class="email-note">You can manage your notification preferences in your <a href="{{ route('settings') }}">account settings</a>.</p>
+
+</x-emails.layout>