Video merge feature, default avatar, video-redirects table, misc UI tweaks

Bundled pre-existing changes on the branch:
- Video merge: controller, service, admin merge modal, and a repair
  console command; new video_redirects table (with source_folder)
  so merged/moved videos keep resolving under their old keys.
- Default avatar SVG for users without a profile picture.
- Assorted view tweaks across profile, video actions/comments/insights,
  admin layout, video-details, and the app layout.
- Small touch-ups in SuperAdminController, User model, NasSyncService.

Co-Authored-By: Claude Opus 4.7 (1M context) <[email protected]>

resources/views/components/video-insights.blade.php

@@ -468,7 +468,7 @@ function renderInsights(d) {
     </div>`).join('');
 
     const recentViewerRows = (d.recent_viewers || []).map(r => {
-        const avatarSrc = r.user_avatar || `https://i.pravatar.cc/150?u=guest-${r.country||'unknown'}`;
+        const avatarSrc = r.user_avatar || '{{ asset('images/default-avatar.svg') }}';
         const title = `Tap for full activity — ${r.user_name}`;
         const safeName = (r.user_name || 'Viewer').replace(/'/g, "\\'");
         return `<div class="ins-dl-user-row" title="${title}"
@@ -554,7 +554,7 @@ function renderInsights(d) {
             : '';
 
         const recentRows = (d.dl_recent||[]).map(r => {
-            const avatarSrc = r.user_avatar || `https://i.pravatar.cc/150?u=guest-${r.country||'unknown'}`;
+            const avatarSrc = r.user_avatar || '{{ asset('images/default-avatar.svg') }}';
             const safeName  = (r.user_name || 'Downloader').replace(/'/g, "\\'");
             const clickAttr = r.user_id
                 ? `onclick="openDownloaderHistory(${r.user_id},'${safeName}','${avatarSrc}')" style="cursor:pointer;" title="See full download history"`