feat(webui): remove reload button (auto-refresh via WebSocket)

feat(webui): remove reload button (auto-refresh via WebSocket)

The WS server pushes refresh notifications on state changes,
making the manual reload button redundant. Remove ReloadButton
component, its styles, tests, and stub. Simplify need-refresh
handler to only reset add-stations toggle (data refresh and
CSTable re-render handled by server notification + watcher).
Remove dead --spacing-xl CSS variable from all themes.