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/imageenc.go

@@ -14,7 +14,8 @@ import (
 	"sneak.berlin/go/pixa/internal/imgcache"
 )
 
-// HandleImageEnc handles requests to /v1/e/{token} for encrypted image URLs.
+// HandleImageEnc handles requests to /v1/e/{token}/* for encrypted image URLs.
+// The trailing path (e.g., /img.jpg) is ignored but helps browsers identify the content type.
 func (s *Handlers) HandleImageEnc() http.HandlerFunc {
 	return func(w http.ResponseWriter, r *http.Request) {
 		ctx := r.Context()