feat(settings): expand About page into a tool management panel

List all managed apps with current/latest versions, with per-tool install
and update buttons plus an Update All action. Installs and updates now run
silently: the button shows a spinner for the full duration, versions refresh
automatically when done, and failures surface the backend error detail in a
toast.

While loading, the button keeps its label and only swaps the icon for a
spinner, so width stays constant across zh/en/ja instead of jumping when the
text changes (e.g. Update -> Updating...).

Also collapses and renames the install-commands area to Manual Install
Commands, and removes the managed-apps badge row and the Install Missing
batch button.