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/services/badnote_server_client.dart

@@ -0,0 +1,139 @@
+// HTTP client for the optional self-hosted BadNote Server (/api/v1).
+// WebDAV remains the primary NAS sync path; this client covers health, auth,
+// vault manifest assist, and OCR job submit/poll.
+
+import 'dart:convert';
+
+import 'package:http/http.dart' as http;
+import 'package:shared_preferences/shared_preferences.dart';
+
+class BadNoteServerConfig {
+  const BadNoteServerConfig({
+    this.baseUrl = '',
+    this.username = '',
+    this.password = '',
+    this.token = '',
+    this.userId = '',
+  });
+
+  final String baseUrl;
+  final String username;
+  final String password;
+  final String token;
+  final String userId;
+
+  bool get isConfigured => baseUrl.trim().isNotEmpty;
+  bool get isLoggedIn => token.isNotEmpty;
+
+  Uri? uri(String path) {
+    final base = baseUrl.trim().replaceAll(RegExp(r'/+$'), '');
+    if (base.isEmpty) return null;
+    final p = path.startsWith('/') ? path : '/$path';
+    return Uri.parse('$base$p');
+  }
+
+  BadNoteServerConfig copyWith({
+    String? baseUrl,
+    String? username,
+    String? password,
+    String? token,
+    String? userId,
+  }) =>
+      BadNoteServerConfig(
+        baseUrl: baseUrl ?? this.baseUrl,
+        username: username ?? this.username,
+        password: password ?? this.password,
+        token: token ?? this.token,
+        userId: userId ?? this.userId,
+      );
+
+  static const _kBase = 'badnote.server.baseUrl';
+  static const _kUser = 'badnote.server.username';
+  static const _kPass = 'badnote.server.password';
+  static const _kToken = 'badnote.server.token';
+  static const _kUid = 'badnote.server.userId';
+
+  static Future<BadNoteServerConfig> load(SharedPreferences prefs) async {
+    return BadNoteServerConfig(
+      baseUrl: prefs.getString(_kBase) ?? '',
+      username: prefs.getString(_kUser) ?? '',
+      password: prefs.getString(_kPass) ?? '',
+      token: prefs.getString(_kToken) ?? '',
+      userId: prefs.getString(_kUid) ?? '',
+    );
+  }
+
+  Future<void> save(SharedPreferences prefs) async {
+    await prefs.setString(_kBase, baseUrl);
+    await prefs.setString(_kUser, username);
+    await prefs.setString(_kPass, password);
+    await prefs.setString(_kToken, token);
+    await prefs.setString(_kUid, userId);
+  }
+}
+
+class BadNoteServerClient {
+  BadNoteServerClient(this.config, {http.Client? httpClient})
+      : _http = httpClient ?? http.Client();
+
+  BadNoteServerConfig config;
+  final http.Client _http;
+
+  Map<String, String> get _authHeaders => {
+        if (config.token.isNotEmpty) 'Authorization': 'Bearer ${config.token}',
+      };
+
+  Future<Map<String, dynamic>> health() async {
+    final uri = config.uri('/api/v1/health');
+    if (uri == null) throw StateError('server URL not set');
+    final res = await _http.get(uri).timeout(const Duration(seconds: 8));
+    if (res.statusCode != 200) {
+      throw StateError('health ${res.statusCode}: ${res.body}');
+    }
+    return jsonDecode(res.body) as Map<String, dynamic>;
+  }
+
+  Future<BadNoteServerConfig> registerOrLogin({
+    required String username,
+    required String password,
+  }) async {
+    final registerUri = config.uri('/api/v1/auth/register');
+    if (registerUri == null) throw StateError('server URL not set');
+    var res = await _http.post(
+      registerUri,
+      headers: {'Content-Type': 'application/json'},
+      body: jsonEncode({'username': username, 'password': password}),
+    );
+    if (res.statusCode == 409) {
+      final loginUri = config.uri('/api/v1/auth/login')!;
+      res = await _http.post(
+        loginUri,
+        headers: {'Content-Type': 'application/json'},
+        body: jsonEncode({'username': username, 'password': password}),
+      );
+    }
+    if (res.statusCode != 200 && res.statusCode != 201) {
+      throw StateError('auth ${res.statusCode}: ${res.body}');
+    }
+    final body = jsonDecode(res.body) as Map<String, dynamic>;
+    config = config.copyWith(
+      username: username,
+      password: password,
+      token: body['token'] as String? ?? '',
+      userId: body['user_id'] as String? ?? '',
+    );
+    return config;
+  }
+
+  Future<Map<String, dynamic>> vaultManifest() async {
+    final uri = config.uri('/api/v1/vault/manifest');
+    if (uri == null) throw StateError('server URL not set');
+    final res = await _http.get(uri, headers: _authHeaders);
+    if (res.statusCode != 200) {
+      throw StateError('manifest ${res.statusCode}: ${res.body}');
+    }
+    return jsonDecode(res.body) as Map<String, dynamic>;
+  }
+
+  void close() => _http.close();
+}