Add share-video-by-email feature

New POST /videos/{video}/share/email route (auth + throttled) handled by
VideoController@shareByEmail, sending the VideoShared mailable rendered from
emails/video-shared.blade.php. Wired into the share modal and video-actions.

Co-Authored-By: Claude Opus 4.7 <[email protected]>

app/Mail/VideoShared.php

@@ -0,0 +1,46 @@
+<?php
+
+namespace App\Mail;
+
+use App\Models\User;
+use App\Models\Video;
+use Illuminate\Bus\Queueable;
+use Illuminate\Mail\Mailable;
+use Illuminate\Mail\Mailables\Address;
+use Illuminate\Mail\Mailables\Content;
+use Illuminate\Mail\Mailables\Envelope;
+use Illuminate\Queue\SerializesModels;
+
+class VideoShared extends Mailable
+{
+    use Queueable, SerializesModels;
+
+    public string $shareTitle;
+
+    public function __construct(
+        public Video $video,
+        public string $shareUrl,
+        public User $sender,
+        public ?string $personalMessage = null,
+        ?string $shareTitle = null,
+    ) {
+        // Version-aware title (e.g. the English track's title) with a primary fallback.
+        $this->shareTitle = $shareTitle ?: $video->title;
+    }
+
+    public function envelope(): Envelope
+    {
+        return new Envelope(
+            subject: $this->sender->name . ' shared "' . $this->shareTitle . '" with you on ' . config('app.name'),
+            // Let the recipient reply straight to the friend who sent it.
+            replyTo: $this->sender->email
+                ? [new Address($this->sender->email, $this->sender->name)]
+                : [],
+        );
+    }
+
+    public function content(): Content
+    {
+        return new Content(view: 'emails.video-shared');
+    }
+}