Improve video sharing by displaying thumbnails correctly on social media

Implements signed thumbnail URLs using Bunny.net and updates og:image meta tags in video.tsx and creates a /thumbnail/:videoId route.

Replit-Commit-Author: Agent
Replit-Commit-Session-Id: 50814a1e-92e4-4968-856f-7bc7eedf5e8f
Replit-Commit-Checkpoint-Type: full_checkpoint
Replit-Commit-Screenshot-Url: https://storage.googleapis.com/screenshot-production-us-central1/8cc42625-c1f5-4e43-99bd-77f2c4dedee2/50814a1e-92e4-4968-856f-7bc7eedf5e8f/wwY5Klj

server/bunny.ts

@@ -73,6 +73,11 @@ export class BunnyService {
     return `https://${this.hostname}${path}?token=${token}&expires=${expireTimestamp}`;
   }
 
+  // Public method for generating signed URLs for sharing
+  generatePublicSignedUrl(path: string, expiryHours: number = 1): string {
+    return this.generateSignedUrl(path, expiryHours);
+  }
+
   private bunnyVideoToVideo(bunnyVideo: BunnyVideo): Video {
     // Generate signed URLs for private video access
     const videoPath = `/${bunnyVideo.guid}/playlist.m3u8`;