feat(oxibadge): add settings screen for shifts, rounding and language

Add a settings screen (gear button on the month-confirmation screen)
to configure the expected shift times, the rounding step, the
interface language, and the time clock address — replacing the old
onboarding-only connection flow. Settings persist to the same
preferences.toml as the reader address, under a single load_settings/
save_settings command pair.

The review screen's "fix shifts" action now redistributes stacked
punches by nearest configured shift time instead of blind position,
and a stacked cell manually cleared down to one entry no longer
leaves a dangling empty input.

Assisted-by: Claude Sonnet 5 <noreply@anthropic.com>

oxibadge/src/lib/components/Onboarding.svelte

@@ -2,6 +2,7 @@
   import { invoke } from '@tauri-apps/api/core';
   import { _ } from 'svelte-i18n';
   import { error, setError, clearError } from '$lib/error';
+  import type { Settings } from '$lib/settings';
   import Column from './Column.svelte';
   import Intro from './Intro.svelte';
   import Field from './Field.svelte';
@@ -28,7 +29,8 @@
     clearError();
     try {
       await invoke('test_connection', { host: trimmedHost, port });
-      await invoke('save_preferences', { host: trimmedHost, port });
+      const settings = await invoke<Settings>('load_settings');
+      await invoke('save_settings', { settings: { ...settings, reader: { host: trimmedHost, port } } });
       onconnected({ host: trimmedHost, port });
     } catch (err) {
       setError(err);