Settings Form

• `SettingsForm`: a react-aria Form that only shows state the app owns, so react-hook-form or any other form state fits: isDirty (enables Save and Discard), isPending (spinner on Save, aria-busy) and onReset (adds a Discard button that should restore the saved values).
• `SettingsSection`: groups fields under a title and description (a labelled group) stacked above them, leaving the width to the fields next to an app sidebar. The fields fall into a two-column grid when there's room (container query); col-span-full takes the whole row.
• `SettingsFormFooter`: a save bar stuck to the bottom of the viewport with a polite status line (no changes / unsaved / saving), optional children before the buttons, Discard and Save.

Warning before leaving with unsaved changes stays in the app, since it depends on the router; use confirm-dialog.

Built-in text is in English; translate it with i18n.labels.