Allow explicit retry of failed native preview preparation

docs/MEDIA-PREVIEW.md

@@ -19,6 +19,10 @@ Arbitrary paths, remote URLs, query strings and traversal are not preview grants
 The generic Tauri asset protocol is disabled in the new configuration.
 Index-change notifications also advance the preview selection identity, so a
 same-path image/recording reloads rather than retaining previously decoded media.
+Failed native preview preparation now offers an explicit **Retry preview**
+button. It invalidates the old request revision and cannot restart a selection
+that has since changed. There is no automatic retry loop. The added regression
+passed with all 60 frontend tests, formatting and the production frontend build.
 
 This does not hash every recording on every request. A same-size/mtime in-place
 write may remain undetected until a filesystem hint or byte-verifying rescan