feat(06-01): build task history sheet, wire into TaskFormScreen, add CalendarTaskRow navigation

- Create task_history_sheet.dart: showTaskHistorySheet() modal bottom sheet
- Sheet uses StreamBuilder on watchCompletionsForTask, shows dates in dd.MM.yyyy + HH:mm format
- Empty state: Icons.history + 'Noch nie erledigt' message
- Count summary shown above list when completions exist
- Add Verlauf ListTile to TaskFormScreen (edit mode only) opening history sheet
- Add onTap to CalendarTaskRow navigating to /rooms/:roomId/tasks/:taskId
- All 106 tests pass, zero analyze issues

lib/features/home/presentation/calendar_task_row.dart

@@ -36,6 +36,9 @@ class CalendarTaskRow extends StatelessWidget {
     final task = taskWithRoom.task;
 
     return ListTile(
+      onTap: () => context.go(
+        '/rooms/${taskWithRoom.roomId}/tasks/${taskWithRoom.task.id}',
+      ),
       leading: Checkbox(
         value: false,
         onChanged: (_) => onCompleted(),

lib/features/tasks/presentation/task_form_screen.dart

@@ -10,6 +10,7 @@ import '../../../core/providers/database_provider.dart';
 import '../../../l10n/app_localizations.dart';
 import '../domain/effort_level.dart';
 import '../domain/frequency.dart';
+import 'task_history_sheet.dart';
 import 'task_providers.dart';
 
 /// Full-screen form for task creation and editing.
@@ -186,6 +187,21 @@ class _TaskFormScreenState extends ConsumerState<TaskFormScreen> {
             ),
             const SizedBox(height: 8),
             _buildDueDatePicker(theme),
+
+            // History section (edit mode only)
+            if (widget.isEditing) ...[
+              const SizedBox(height: 24),
+              const Divider(),
+              ListTile(
+                leading: const Icon(Icons.history),
+                title: Text(l10n.taskHistoryTitle),
+                trailing: const Icon(Icons.chevron_right),
+                onTap: () => showTaskHistorySheet(
+                  context: context,
+                  taskId: widget.taskId!,
+                ),
+              ),
+            ],
           ],
         ),
       ),

lib/features/tasks/presentation/task_history_sheet.dart

@@ -0,0 +1,136 @@
+import 'package:flutter/material.dart';
+import 'package:flutter_riverpod/flutter_riverpod.dart';
+import 'package:intl/intl.dart';
+
+import '../../../core/database/database.dart';
+import '../../../core/providers/database_provider.dart';
+import '../../../l10n/app_localizations.dart';
+
+/// Shows a modal bottom sheet displaying the completion history for a task.
+///
+/// The sheet displays all past completions in reverse-chronological order
+/// (newest first). If the task has never been completed, an empty state is shown.
+Future<void> showTaskHistorySheet({
+  required BuildContext context,
+  required int taskId,
+}) {
+  return showModalBottomSheet<void>(
+    context: context,
+    isScrollControlled: true,
+    builder: (context) => _TaskHistorySheet(taskId: taskId),
+  );
+}
+
+class _TaskHistorySheet extends ConsumerWidget {
+  const _TaskHistorySheet({required this.taskId});
+
+  final int taskId;
+
+  @override
+  Widget build(BuildContext context, WidgetRef ref) {
+    final theme = Theme.of(context);
+    final colorScheme = theme.colorScheme;
+    final l10n = AppLocalizations.of(context);
+
+    return SafeArea(
+      child: Padding(
+        padding: const EdgeInsets.all(16),
+        child: Column(
+          mainAxisSize: MainAxisSize.min,
+          children: [
+            // Drag handle
+            Container(
+              width: 32,
+              height: 4,
+              margin: const EdgeInsets.only(bottom: 16),
+              decoration: BoxDecoration(
+                color: colorScheme.onSurfaceVariant.withValues(alpha: 0.4),
+                borderRadius: BorderRadius.circular(2),
+              ),
+            ),
+            // Title
+            Text(
+              l10n.taskHistoryTitle,
+              style: theme.textTheme.titleMedium,
+            ),
+            const SizedBox(height: 16),
+            // Completion list via StreamBuilder
+            StreamBuilder<List<TaskCompletion>>(
+              stream: ref
+                  .read(appDatabaseProvider)
+                  .tasksDao
+                  .watchCompletionsForTask(taskId),
+              builder: (context, snapshot) {
+                if (!snapshot.hasData) {
+                  return const Center(child: CircularProgressIndicator());
+                }
+
+                final completions = snapshot.data!;
+
+                if (completions.isEmpty) {
+                  return Column(
+                    mainAxisSize: MainAxisSize.min,
+                    children: [
+                      Icon(
+                        Icons.history,
+                        size: 48,
+                        color: colorScheme.onSurfaceVariant,
+                      ),
+                      const SizedBox(height: 8),
+                      Text(
+                        l10n.taskHistoryEmpty,
+                        style: theme.textTheme.bodyLarge?.copyWith(
+                          color: colorScheme.onSurfaceVariant,
+                        ),
+                      ),
+                    ],
+                  );
+                }
+
+                // Show count summary
+                return Column(
+                  mainAxisSize: MainAxisSize.min,
+                  children: [
+                    Text(
+                      l10n.taskHistoryCount(completions.length),
+                      style: theme.textTheme.bodyMedium?.copyWith(
+                        color: colorScheme.onSurfaceVariant,
+                      ),
+                    ),
+                    const SizedBox(height: 8),
+                    ConstrainedBox(
+                      constraints: BoxConstraints(
+                        maxHeight:
+                            MediaQuery.of(context).size.height * 0.4,
+                      ),
+                      child: ListView.builder(
+                        shrinkWrap: true,
+                        itemCount: completions.length,
+                        itemBuilder: (context, index) {
+                          final completion = completions[index];
+                          final dateStr = DateFormat('dd.MM.yyyy', 'de')
+                              .format(completion.completedAt);
+                          final timeStr = DateFormat('HH:mm', 'de')
+                              .format(completion.completedAt);
+                          return ListTile(
+                            leading: Icon(
+                              Icons.check_circle_outline,
+                              color: colorScheme.primary,
+                            ),
+                            title: Text(dateStr),
+                            subtitle: Text(timeStr),
+                          );
+                        },
+                      ),
+                    ),
+                  ],
+                );
+              },
+            ),
+            const SizedBox(height: 8),
+          ],
+        ),
+      ),
+    );
+  }
+}