* feat(settings): add a manual widget update button

General > Updates can check for and install a widget update on demand,
even with automatic checks off.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

* fix(settings): run manual widget updates in the applet

Settings now only request a check or install through a runtime config key;
the applet's updater runs it, so closing the dialog cannot cut an install
short and manual and automatic runs never overlap. The found release
version is persisted, survives a failed install for retry, and gets its own
Install button next to Check.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

* fix(settings): keep the found widget release after a restart

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

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Co-authored-by: Claude Opus 5.5 <noreply@anthropic.com>