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/lib/components/Onboarding.svelte

@@ -1,6 +1,7 @@
 <script lang="ts">
   import { invoke } from '@tauri-apps/api/core';
   import { _ } from 'svelte-i18n';
+  import { error, setError, clearError } from '$lib/error';
   import Column from './Column.svelte';
   import Intro from './Intro.svelte';
   import Field from './Field.svelte';
@@ -10,40 +11,29 @@
 
   let { onconnected }: { onconnected: (cfg: { host: string; port: number }) => void } = $props();
 
-  type Phase = 'idle' | 'testing' | 'err';
-
   let host = $state('');
   let port = $state(5005);
-  let phase = $state<Phase>('idle');
-  let errorCode = $state('');
+  let testing = $state(false);
 
   const trimmedHost = $derived(host.trim());
   const empty = $derived(trimmedHost === '');
-  const disabled = $derived(empty || phase === 'testing');
+  const disabled = $derived(empty || testing);
   const btnLabel = $derived(
-    phase === 'testing'
-      ? $_('onboarding.button.testing')
-      : phase === 'err'
-        ? $_('onboarding.button.retry')
-        : $_('onboarding.button.idle')
+    testing ? $_('onboarding.button.testing') : $error ? $_('onboarding.button.retry') : $_('onboarding.button.idle')
   );
 
-  function resetPhase() {
-    phase = 'idle';
-    errorCode = '';
-  }
-
   async function testAndSave() {
     if (disabled) return;
-    phase = 'testing';
-    errorCode = '';
+    testing = true;
+    clearError();
     try {
       await invoke('test_connection', { host: trimmedHost, port });
       await invoke('save_preferences', { host: trimmedHost, port });
       onconnected({ host: trimmedHost, port });
     } catch (err) {
-      errorCode = String(err);
-      phase = 'err';
+      setError(err);
+    } finally {
+      testing = false;
     }
   }
 </script>
@@ -64,7 +54,7 @@
         label={$_('onboarding.host_label')}
         bind:value={host}
         placeholder="192.168.1.100"
-        oninput={resetPhase}
+        oninput={clearError}
       >
         {#snippet icon()}
           <svg width="18" height="18" viewBox="0 0 24 24" aria-hidden="true">
@@ -79,14 +69,14 @@
         bind:value={port}
         type="number"
         placeholder="5005"
-        oninput={resetPhase}
+        oninput={clearError}
       />
     </div>
 
-    <Button type="submit" label={btnLabel} faded={empty} busy={phase === 'testing'} {disabled} />
+    <Button type="submit" label={btnLabel} faded={empty} busy={testing} {disabled} />
 
-    {#if phase === 'err'}
-      <ErrorBanner title={$_('onboarding.error_title')} message={$_(`onboarding.errors.${errorCode}`)} />
+    {#if $error}
+      <ErrorBanner title={$_('errors.title')} message={$error} />
     {/if}
 
     <Hint text={$_('onboarding.hint')} />