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]>

database/migrations/2026_07_30_000001_create_video_redirects_table.php

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+<?php
+
+use Illuminate\Database\Migrations\Migration;
+use Illuminate\Database\Schema\Blueprint;
+use Illuminate\Support\Facades\Schema;
+
+return new class extends Migration {
+    public function up(): void
+    {
+        Schema::create('video_redirects', function (Blueprint $table) {
+            $table->id();
+            $table->unsignedBigInteger('source_id')->unique();
+            $table->foreignId('target_id')->constrained('videos')->cascadeOnDelete();
+            $table->timestamp('created_at')->nullable();
+            $table->index('target_id');
+        });
+    }
+
+    public function down(): void
+    {
+        Schema::dropIfExists('video_redirects');
+    }
+};

database/migrations/2026_07_30_000002_add_source_folder_to_video_redirects.php

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+<?php
+
+use Illuminate\Database\Migrations\Migration;
+use Illuminate\Database\Schema\Blueprint;
+use Illuminate\Support\Facades\Schema;
+
+return new class extends Migration {
+    public function up(): void
+    {
+        Schema::table('video_redirects', function (Blueprint $table) {
+            $table->string('source_folder', 500)->nullable()->after('target_id');
+        });
+    }
+
+    public function down(): void
+    {
+        Schema::table('video_redirects', function (Blueprint $table) {
+            $table->dropColumn('source_folder');
+        });
+    }
+};