feat(backend): enhance social previews for single-file shares

Implements dynamic Open Graph (OG) metadata and image generation for
single-file shared boxes to improve social media previews.

Changes include:
- Added a new route `/d/{boxID}/f/{fileID}/og-image.jpg` for file-specific OG images.
- Updated `DownloadPage` to dynamically set the page title, description, and OG image properties when a box contains only one file.
- Restricted raw media inline serving for social bots to images and videos.
- Added helper functions to format file share descriptions and determine appropriate social image URLs and types.
- Integrated basic font rendering to support dynamic OG image generation.

backend/libs/web/renderer.go

@@ -23,10 +23,14 @@ type PageData struct {
 	BaseURL      string
 	CanonicalURL string
 	Robots       string
+	OGType       string
 	Title        string
 	Description  string
 	ImageURL     string
 	ImageAlt     string
+	ImageType    string
+	MediaURL     string
+	MediaType    string
 	CurrentYear  int
 	CurrentUser  any
 	CSRFToken    string