fix(oxibadge): show connection errors instead of failing silently

load_records/load_employees failures were only logged to the console
and silently reset the UI to the month picker. Errors now flow through
a shared store (src/lib/error.ts) into an ErrorBanner, reused by both
Onboarding and ConfirmMonth, with the raw message passed straight
through from Rust (no stable-code classification layer — these are
mostly plain I/O errors, not worth categorizing).

i18n stays grouped per screen as before, with error-related strings
split into their own top-level "errors" group.

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

oxibadge/src/routes/+page.svelte

@@ -3,6 +3,7 @@
   import { onMount } from 'svelte';
   import { _, locale } from 'svelte-i18n';
   import { monthName } from '$lib/month';
+  import { setError, clearError } from '$lib/error';
   import Screen from '$lib/components/Screen.svelte';
   import Onboarding from '$lib/components/Onboarding.svelte';
   import ConfirmMonth from '$lib/components/ConfirmMonth.svelte';
@@ -25,13 +26,14 @@
     selectedYear = selection.year;
     selectedMonth = selection.month;
     step = 'loading-records';
+    clearError();
     try {
       const records = await invoke('load_records', selection);
       step = 'loading-employees';
       await invoke('load_employees', { records });
       step = 'done';
     } catch (err) {
-      console.error(err);
+      setError(err);
       step = 'confirm-month';
     }
   }