feat(02-04): create template picker bottom sheet with German localization

- Add TemplatePickerSheet StatefulWidget with checklist UI for task templates
- Add showTemplatePickerSheet helper for modal display with DraggableScrollableSheet
- Add 4 German localization keys: templatePickerTitle, Skip, Add, Selected count
- All templates unchecked by default, confirm button only enabled with selection

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

lib/l10n/app_de.arb

@@ -59,5 +59,14 @@
   "taskDeleteConfirmAction": "L\u00f6schen",
   "taskEmptyTitle": "Noch keine Aufgaben",
   "taskEmptyMessage": "Erstelle die erste Aufgabe f\u00fcr diesen Raum.",
-  "taskEmptyAction": "Aufgabe erstellen"
+  "taskEmptyAction": "Aufgabe erstellen",
+  "templatePickerTitle": "Aufgaben aus Vorlagen hinzuf\u00fcgen?",
+  "templatePickerSkip": "\u00dcberspringen",
+  "templatePickerAdd": "Hinzuf\u00fcgen",
+  "templatePickerSelected": "{count} ausgew\u00e4hlt",
+  "@templatePickerSelected": {
+    "placeholders": {
+      "count": { "type": "int" }
+    }
+  }
 }

lib/l10n/app_localizations.dart

@@ -393,6 +393,30 @@ abstract class AppLocalizations {
   /// In de, this message translates to:
   /// **'Aufgabe erstellen'**
   String get taskEmptyAction;
+
+  /// No description provided for @templatePickerTitle.
+  ///
+  /// In de, this message translates to:
+  /// **'Aufgaben aus Vorlagen hinzuf\u00fcgen?'**
+  String get templatePickerTitle;
+
+  /// No description provided for @templatePickerSkip.
+  ///
+  /// In de, this message translates to:
+  /// **'\u00dcberspringen'**
+  String get templatePickerSkip;
+
+  /// No description provided for @templatePickerAdd.
+  ///
+  /// In de, this message translates to:
+  /// **'Hinzuf\u00fcgen'**
+  String get templatePickerAdd;
+
+  /// No description provided for @templatePickerSelected.
+  ///
+  /// In de, this message translates to:
+  /// **'{count} ausgew\u00e4hlt'**
+  String templatePickerSelected(int count);
 }
 
 class _AppLocalizationsDelegate

lib/l10n/app_localizations_de.dart

@@ -164,4 +164,18 @@ class AppLocalizationsDe extends AppLocalizations {
 
   @override
   String get taskEmptyAction => 'Aufgabe erstellen';
+
+  @override
+  String get templatePickerTitle => 'Aufgaben aus Vorlagen hinzuf\u00fcgen?';
+
+  @override
+  String get templatePickerSkip => '\u00dcberspringen';
+
+  @override
+  String get templatePickerAdd => 'Hinzuf\u00fcgen';
+
+  @override
+  String templatePickerSelected(int count) {
+    return '$count ausgew\u00e4hlt';
+  }
 }