feat(03-01): add daily plan provider with date categorization and localization keys

- dailyPlanProvider: manual StreamProvider.autoDispose with overdue/today/tomorrow partitioning
- Stable progress denominator: remaining overdue + remaining today + completedTodayCount
- 10 new German localization keys for daily plan sections, progress, empty states
- dart analyze clean, full test suite (66/66) passes

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

lib/l10n/app_localizations.dart

@@ -417,6 +417,60 @@ abstract class AppLocalizations {
   /// In de, this message translates to:
   /// **'{count} ausgewählt'**
   String templatePickerSelected(int count);
+
+  /// No description provided for @dailyPlanProgress.
+  ///
+  /// In de, this message translates to:
+  /// **'{completed} von {total} erledigt'**
+  String dailyPlanProgress(int completed, int total);
+
+  /// No description provided for @dailyPlanSectionOverdue.
+  ///
+  /// In de, this message translates to:
+  /// **'Überfällig'**
+  String get dailyPlanSectionOverdue;
+
+  /// No description provided for @dailyPlanSectionToday.
+  ///
+  /// In de, this message translates to:
+  /// **'Heute'**
+  String get dailyPlanSectionToday;
+
+  /// No description provided for @dailyPlanSectionUpcoming.
+  ///
+  /// In de, this message translates to:
+  /// **'Demnächst'**
+  String get dailyPlanSectionUpcoming;
+
+  /// No description provided for @dailyPlanUpcomingCount.
+  ///
+  /// In de, this message translates to:
+  /// **'Demnächst ({count})'**
+  String dailyPlanUpcomingCount(int count);
+
+  /// No description provided for @dailyPlanAllClearTitle.
+  ///
+  /// In de, this message translates to:
+  /// **'Alles erledigt! 🌟'**
+  String get dailyPlanAllClearTitle;
+
+  /// No description provided for @dailyPlanAllClearMessage.
+  ///
+  /// In de, this message translates to:
+  /// **'Keine Aufgaben für heute. Genieße den Moment!'**
+  String get dailyPlanAllClearMessage;
+
+  /// No description provided for @dailyPlanNoOverdue.
+  ///
+  /// In de, this message translates to:
+  /// **'Keine überfälligen Aufgaben'**
+  String get dailyPlanNoOverdue;
+
+  /// No description provided for @dailyPlanNoTasks.
+  ///
+  /// In de, this message translates to:
+  /// **'Noch keine Aufgaben angelegt'**
+  String get dailyPlanNoTasks;
 }
 
 class _AppLocalizationsDelegate