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]>

app/Http/Controllers/VideoMergeController.php

@@ -0,0 +1,98 @@
+<?php
+
+namespace App\Http\Controllers;
+
+use App\Models\Video;
+use App\Services\VideoMergeService;
+use Illuminate\Http\Request;
+use Illuminate\Support\Facades\Auth;
+
+class VideoMergeController extends Controller
+{
+    public function __construct(private VideoMergeService $merger) {}
+
+    /**
+     * List the current user's other music videos that $target can be merged with.
+     */
+    public function candidates(Request $request, Video $target)
+    {
+        $this->authorizeOwner($target);
+        if ($target->type !== 'music') {
+            return response()->json(['error' => 'Only music videos can be merged.'], 422);
+        }
+
+        $q = trim((string) $request->query('q', ''));
+        $query = Video::where('user_id', Auth::id())
+            ->where('type', 'music')
+            ->where('id', '!=', $target->id)
+            ->orderByDesc('created_at');
+        if ($q !== '') {
+            $query->where('title', 'like', '%' . $q . '%');
+        }
+        $items = $query->limit(30)->get(['id', 'title', 'thumbnail', 'created_at'])->map(function ($v) {
+            return [
+                'id'        => $v->getRouteKey(),
+                'title'     => $v->title,
+                'thumbnail' => $v->thumbnail_url,
+                'created'   => $v->created_at?->diffForHumans(),
+            ];
+        });
+
+        return response()->json(['items' => $items]);
+    }
+
+    public function preview(Video $target, Video $source)
+    {
+        $this->authorizeOwner($target);
+        $this->authorizeOwner($source);
+        if ($target->type !== 'music' || $source->type !== 'music') {
+            return response()->json(['error' => 'Only music videos can be merged.'], 422);
+        }
+        if ($target->id === $source->id) {
+            return response()->json(['error' => 'Cannot merge a video with itself.'], 422);
+        }
+
+        return response()->json([
+            'source' => [
+                'id'    => $source->getRouteKey(),
+                'title' => $source->title,
+                'thumb' => $source->thumbnail_url,
+            ],
+            'target' => [
+                'id'    => $target->getRouteKey(),
+                'title' => $target->title,
+                'thumb' => $target->thumbnail_url,
+            ],
+            'counts' => $this->merger->preview($source, $target),
+        ]);
+    }
+
+    public function merge(Request $request, Video $target, Video $source)
+    {
+        $this->authorizeOwner($target);
+        $this->authorizeOwner($source);
+
+        try {
+            $this->merger->merge($source, $target);
+        } catch (\Throwable $e) {
+            \Log::error('Video merge failed', [
+                'source' => $source->id,
+                'target' => $target->id,
+                'err'    => $e->getMessage(),
+            ]);
+            return response()->json(['error' => 'Merge failed: ' . $e->getMessage()], 500);
+        }
+
+        return response()->json([
+            'ok'       => true,
+            'redirect' => route('videos.show', $target),
+        ]);
+    }
+
+    private function authorizeOwner(Video $video): void
+    {
+        $user = Auth::user();
+        if (!$user) abort(401);
+        if ($user->id !== $video->user_id && !$user->isSuperAdmin()) abort(403);
+    }
+}