fix(chat): fix ChatBloc event callback and test reliability

- Fix onEvent callback initialization in ChatBloc constructor
- Add MockAgUiService to isolate test from mock API behavior
- Remove unnecessary non-null assertions in tests

apps/lib/features/chat/data/ai/ai_decision_engine.dart

@@ -2,17 +2,23 @@ import 'dart:convert';
 
 enum Intent { createEvent, searchEvent, unknown }
 
-class AiDecisionEngine {
-  /// 意图匹配规则（顺序敏感：searchEvent 优先级高于 createEvent）
-  static final List<(RegExp, Intent)> _orderedPatterns = [
-    (RegExp(r'^查看|^有什么|^今天.*日程|^明天.*安排|^查询'), Intent.searchEvent),
-    (RegExp(r'提醒|开会|预约|安排.*时间|创建.*日程'), Intent.createEvent),
-    (
-      RegExp(r'明天.*\d|今天.*\d|后天.*\d|\d{1,2}点|\d{1,2}:\d{2}'),
-      Intent.createEvent,
-    ),
-  ];
+/// 意图匹配规则（顺序敏感：searchEvent 优先级高于 createEvent）
+final _orderedPatterns = <(RegExp, Intent)>[
+  (RegExp(r'^查看|^有什么|^今天.*日程|^明天.*安排|^查询'), Intent.searchEvent),
+  (RegExp(r'提醒|开会|预约|安排.*时间|创建.*日程'), Intent.createEvent),
+  (RegExp(r'明天.*\d|今天.*\d|后天.*\d|\d{1,2}点|\d{1,2}:\d{2}'), Intent.createEvent),
+];
 
+/// 时区常量
+const _defaultTimezone = 'Asia/Shanghai';
+const _dayToday = '今天';
+const _dayTomorrow = '明天';
+const _dayAfterTomorrow = '后天';
+const _tomorrowOffset = 1;
+const _dayAfterTomorrowOffset = 2;
+const _defaultMinute = 0;
+
+class AiDecisionEngine {
   Intent matchIntent(String text) {
     for (final (pattern, intent) in _orderedPatterns) {
       if (pattern.hasMatch(text)) return intent;
@@ -34,31 +40,33 @@ class AiDecisionEngine {
           .trim();
     }
 
-    if (args['title'] == null || (args['title'] as String).isEmpty) return null;
+    final title = args['title'];
+    if (title == null || (title as String).isEmpty) return null;
 
     final timeMatch = RegExp(
       r'(明天|今天|后天)?\s*(\d{1,2})[:点](\d{2})?',
     ).firstMatch(text);
     if (timeMatch != null) {
-      final dayStr = timeMatch.group(1) ?? '今天';
+      final dayStr = timeMatch.group(1) ?? _dayToday;
       final hour = int.parse(timeMatch.group(2)!);
-      final minute = int.parse(timeMatch.group(3) ?? '0');
+      final minute = int.parse(timeMatch.group(3) ?? '$_defaultMinute');
 
       final now = DateTime.now();
-      DateTime startAt;
-      switch (dayStr) {
-        case '明天':
-          startAt = DateTime(now.year, now.month, now.day + 1, hour, minute);
-          break;
-        case '后天':
-          startAt = DateTime(now.year, now.month, now.day + 2, hour, minute);
-          break;
-        default:
-          startAt = DateTime(now.year, now.month, now.day, hour, minute);
-      }
+      final dayOffset = switch (dayStr) {
+        _dayTomorrow => _tomorrowOffset,
+        _dayAfterTomorrow => _dayAfterTomorrowOffset,
+        _ => 0,
+      };
+      final startAt = DateTime(
+        now.year,
+        now.month,
+        now.day + dayOffset,
+        hour,
+        minute,
+      );
 
       args['startAt'] = startAt.toIso8601String();
-      args['timezone'] = 'Asia/Shanghai';
+      args['timezone'] = _defaultTimezone;
     }
 
     if (!args.containsKey('startAt')) return null;