feat: add table_calendar package and CalendarEvent model with tests

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

lib/data/models/calendar_event.dart

@@ -0,0 +1,47 @@
+class CalendarEvent {
+  final int id;
+  final String title;
+  final DateTime startDt;
+  final DateTime? endDt;
+  final bool allDay;
+  final String description;
+  final String location;
+  final String color;
+  final String? recurrence;
+  final int? projectId;
+  final int? reminderMinutes;
+
+  const CalendarEvent({
+    required this.id,
+    required this.title,
+    required this.startDt,
+    this.endDt,
+    required this.allDay,
+    required this.description,
+    required this.location,
+    required this.color,
+    this.recurrence,
+    this.projectId,
+    this.reminderMinutes,
+  });
+
+  factory CalendarEvent.fromJson(Map<String, dynamic> json) => CalendarEvent(
+        id: json['id'] as int,
+        title: json['title'] as String? ?? '',
+        startDt: DateTime.parse(json['start_dt'] as String),
+        endDt: json['end_dt'] != null
+            ? DateTime.parse(json['end_dt'] as String)
+            : null,
+        allDay: json['all_day'] as bool? ?? false,
+        description: json['description'] as String? ?? '',
+        location: json['location'] as String? ?? '',
+        color: json['color'] as String? ?? '',
+        recurrence: json['recurrence'] as String?,
+        projectId: json['project_id'] as int?,
+        reminderMinutes: json['reminder_minutes'] as int?,
+      );
+}
+
+/// Strips time from a DateTime, returning midnight local.
+/// Used as map keys in CalendarState.eventsByDay.
+DateTime dateOnly(DateTime dt) => DateTime(dt.year, dt.month, dt.day);