Feature: control download button visibility for files inside archives

[wybaby168]

Summary

Add an option to control whether the download button is shown when previewing a file from inside an archive.

Background

The archive renderer currently lets users open supported entries and preview them inline. Some enterprise deployments need finer-grained control over actions exposed for nested archive entries, especially when the outer archive can be viewed but extracted content should not always be downloadable.

Proposed behavior

• Provide a documented option to show or hide the download button for archive entries.
• Keep the top-level viewer download behavior independent from nested archive entry behavior.
• Support a global boolean as the simple path, and consider a callback/policy hook for per-entry decisions.
• Ensure the state is reflected consistently in the archive preview header and any compact/mobile toolbar.

Suggested API shape

const viewer = createFileViewer(container, {
  archive: {
    entryActions: {
      download: false,
    },
  },
})

A callback form may be useful for enterprise policies:

archive: {
  entryActions: {
    download(entry) {
      return entry.path.startsWith('public/')
    },
  },
}

Acceptance criteria

• Consumers can hide the nested file download button without disabling the viewer-level download action.
• The option works for archive entries previewed through the archive renderer.
• The default behavior remains backward-compatible.
• Documentation and demo examples mention the option.
• A focused harness or smoke case verifies both visible and hidden states.