feat(programmer): day rows builder + work-log workDate

- Add workDate field to ProgrammerTaskWorkLog (defaults to Manila day of createdAt)
- Add deltaJsonToPlainText function to quill_field.dart for Delta/plain text conversion
- Implement buildDayRows function to generate day sheet rows with proper sorting
- Implement DaySheetRow serialization and deserialization
- Add comprehensive tests for day rows builder and workDate field
- Verify backward compatibility via existing programmer_task_ledger_test
Co-Authored-By: claude-flow <ruv@ruv.net>

lib/models/programmer_task_work_log.model.dart

@@ -1,4 +1,5 @@
 import '../utils/app_time.dart';
+import '../utils/programmer_daily_time.dart';
 
 /// A work-log entry on a programmer task (plain, online-first model).
 ///
@@ -13,6 +14,7 @@ class ProgrammerTaskWorkLog {
   final String description;
   final int? minutes;
   final DateTime createdAt;
+  final DateTime workDate;
 
   ProgrammerTaskWorkLog({
     required this.id,
@@ -21,16 +23,22 @@ class ProgrammerTaskWorkLog {
     required this.description,
     this.minutes,
     required this.createdAt,
-  });
+    DateTime? workDate,
+  }) : workDate = workDate ?? manilaDay(createdAt);
 
   factory ProgrammerTaskWorkLog.fromMap(Map<String, dynamic> map) {
+    final createdAt = AppTime.parse(map['created_at'] as String);
+    final workDate = map['work_date'] != null
+        ? parseDayKey(map['work_date'] as String)
+        : manilaDay(createdAt);
     return ProgrammerTaskWorkLog(
       id: map['id'].toString(),
       taskId: map['task_id'].toString(),
       authorId: map['author_id'].toString(),
       description: map['description'] as String? ?? '',
       minutes: (map['minutes'] as num?)?.toInt(),
-      createdAt: AppTime.parse(map['created_at'] as String),
+      createdAt: createdAt,
+      workDate: workDate,
     );
   }
 }