feat: vault-aligned server v1 + UX polish

Redesign the optional FastAPI companion around vault files (manifest /
PUT/GET/DELETE + OCR jobs) instead of legacy strokes_json notes. Wire a
client Server settings panel for health/login. Polish shell UX: l10n for
settings/home/board, sticky-board empty state, and a narrow-screen
diagnostics FAB.

Co-authored-by: Cursor <cursoragent@cursor.com>

lib/diagnostics/diagnostic_chrome.dart

@@ -6,6 +6,7 @@ import 'diagnostic_export.dart';
 import '../editor/canvas/input_diagnostics.dart';
 import '../editor/input/diagnostic_logger.dart';
 import '../editor/input/pen_input_service.dart';
+import '../l10n/app_localizations.dart';
 
 /// Shared diagnostics chrome: overlay readout + export action.
 /// Mount on any document surface (note / PDF / PPT / board).
@@ -54,7 +55,7 @@ class DiagnosticChromeState extends State<DiagnosticChrome> {
       ScaffoldMessenger.of(context).showSnackBar(
         SnackBar(
           content: Text(
-            '诊断包已导出 (${result.bytes} bytes)\n路径已复制到剪贴板',
+            AppLocalizations.of(context).diagExported(result.bytes),
           ),
           duration: const Duration(seconds: 5),
         ),
@@ -65,7 +66,9 @@ class DiagnosticChromeState extends State<DiagnosticChrome> {
       });
       if (!mounted) return;
       ScaffoldMessenger.of(context).showSnackBar(
-        SnackBar(content: Text('导出失败: $e')),
+        SnackBar(
+          content: Text(AppLocalizations.of(context).diagExportFail('$e')),
+        ),
       );
     } finally {
       if (mounted) setState(() => _exporting = false);