Change encrypted URL format to /v1/e/{token}/img.{ext}

Add trailing filename to encrypted URLs for better browser compatibility.
The filename is ignored by the server but helps browsers identify content type.

internal/handlers/auth.go

@@ -154,8 +154,14 @@ func (s *Handlers) HandleGenerateURL() http.HandlerFunc {
 			scheme = "http"
 		}
 
+		// Determine file extension for the trailing filename
+		ext := format
+		if ext == "" || ext == "orig" {
+			ext = "jpg" // Default extension
+		}
+
 		host := r.Host
-		generatedURL := scheme + "://" + host + "/v1/e/" + url.PathEscape(token)
+		generatedURL := scheme + "://" + host + "/v1/e/" + url.PathEscape(token) + "/img." + ext
 
 		// Format expiry for display
 		expiresAtStr := "Never"