feat: Add multi-CDN integration for global video delivery

- Create CDN manager with multi-provider support (Bunny, Cloudflare, S3, Backblaze, Wasabi)
- Implement automatic CDN upload and failover system
- Add multi-quality video support (360p-2160p)
- Build quality selector UI with auto-detection
- Track CDN bandwidth usage for cost monitoring
- Implement cache purging API
- Add background CDN upload worker script
- Create comprehensive CDN documentation

Features:
- Multi-CDN support with priority-based failover
- BunnyCDN, Cloudflare R2, AWS S3, Backblaze B2, Wasabi integration
- Multi-quality delivery (adaptive quality selection)
- Auto quality based on connection speed
- User preference persistence
- Bandwidth tracking per provider
- Cache purge API
- Cost optimization strategies
- Production-ready with error handling

f_scripts/fe/css/quality-selector.css

@@ -0,0 +1,82 @@
+/**
+ * Quality Selector Styles
+ */
+
+.quality-selector {
+    position: relative;
+    display: inline-block;
+}
+
+.quality-button {
+    display: flex;
+    align-items: center;
+    gap: 6px;
+    padding: 8px 12px;
+    background: rgba(0, 0, 0, 0.6);
+    color: white;
+    border: none;
+    border-radius: 6px;
+    cursor: pointer;
+    font-size: 14px;
+    font-weight: 500;
+    transition: background 0.2s;
+}
+
+.quality-button:hover {
+    background: rgba(0, 0, 0, 0.8);
+}
+
+.quality-button svg {
+    width: 20px;
+    height: 20px;
+}
+
+.quality-menu {
+    position: absolute;
+    bottom: 100%;
+    right: 0;
+    margin-bottom: 8px;
+    background: rgba(28, 28, 28, 0.95);
+    backdrop-filter: blur(10px);
+    border-radius: 8px;
+    padding: 8px 0;
+    min-width: 120px;
+    box-shadow: 0 4px 16px rgba(0, 0, 0, 0.3);
+    z-index: 1000;
+}
+
+.quality-option {
+    padding: 10px 16px;
+    color: white;
+    cursor: pointer;
+    transition: background 0.2s;
+    font-size: 14px;
+}
+
+.quality-option:hover {
+    background: rgba(255, 255, 255, 0.1);
+}
+
+.quality-option.active {
+    background: rgba(0, 123, 255, 0.3);
+    font-weight: 600;
+}
+
+.quality-option.active::before {
+    content: '✓ ';
+    margin-right: 4px;
+}
+
+/* Mobile styles */
+@media (max-width: 768px) {
+    .quality-menu {
+        position: fixed;
+        bottom: 60px;
+        right: 16px;
+        left: auto;
+    }
+    
+    .quality-button {
+        padding: 10px 14px;
+    }
+}