feat: flexible meal planning wizard — plan 1 meal, 1 day, several days, or a week

Backend:
- migration 005: expand menu_items.meal_type CHECK to all 6 types (second_breakfast, afternoon_snack, snack)
- ai/types.go: add Days and MealTypes to MenuRequest for partial generation
- openai/menu.go: parametrize GenerateMenu — use requested meal types and day count; add caloric fractions for all 6 meal types
- menu/repository.go: add UpsertItemsInTx for partial upsert (preserves existing slots); fix meal_type sort order in GetByWeek
- menu/handler.go: add dates+meal_types path to POST /ai/generate-menu; extract fetchImages/saveRecipes helpers; returns {"plans":[...]} for dates mode; backward-compatible with week mode

Client:
- PlanMenuSheet: bottom sheet with 4 planning horizon options
- PlanDatePickerSheet: adaptive sheet with date strip (single day/meal) or custom CalendarRangePicker (multi-day/week); sliding 7-day window for week mode
- menu_service.dart: add generateForDates
- menu_provider.dart: add PlanMenuService (generates + invalidates week providers), lastPlannedDateProvider
- home_screen.dart: add _PlanMenuButton card below quick actions; opens planning wizard
- l10n: 16 new keys for planning UI across all 12 languages

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

client/lib/features/menu/plan_menu_sheet.dart

@@ -0,0 +1,101 @@
+import 'package:flutter/material.dart';
+import 'package:food_ai/l10n/app_localizations.dart';
+
+/// The planning horizon selected by the user.
+enum PlanMode { singleMeal, singleDay, days, week }
+
+/// Bottom sheet that lets the user choose a planning horizon.
+/// Closes itself and calls [onModeSelected] with the chosen mode.
+class PlanMenuSheet extends StatelessWidget {
+  const PlanMenuSheet({super.key, required this.onModeSelected});
+
+  final void Function(PlanMode mode) onModeSelected;
+
+  @override
+  Widget build(BuildContext context) {
+    final l10n = AppLocalizations.of(context)!;
+    final theme = Theme.of(context);
+
+    return SafeArea(
+      child: Padding(
+        padding: const EdgeInsets.fromLTRB(16, 20, 16, 16),
+        child: Column(
+          mainAxisSize: MainAxisSize.min,
+          crossAxisAlignment: CrossAxisAlignment.stretch,
+          children: [
+            Text(
+              l10n.planMenuTitle,
+              style: theme.textTheme.titleLarge,
+              textAlign: TextAlign.center,
+            ),
+            const SizedBox(height: 20),
+            _PlanOptionTile(
+              icon: Icons.restaurant_outlined,
+              title: l10n.planOptionSingleMeal,
+              subtitle: l10n.planOptionSingleMealDesc,
+              onTap: () => _select(context, PlanMode.singleMeal),
+            ),
+            _PlanOptionTile(
+              icon: Icons.today_outlined,
+              title: l10n.planOptionDay,
+              subtitle: l10n.planOptionDayDesc,
+              onTap: () => _select(context, PlanMode.singleDay),
+            ),
+            _PlanOptionTile(
+              icon: Icons.date_range_outlined,
+              title: l10n.planOptionDays,
+              subtitle: l10n.planOptionDaysDesc,
+              onTap: () => _select(context, PlanMode.days),
+            ),
+            _PlanOptionTile(
+              icon: Icons.calendar_month_outlined,
+              title: l10n.planOptionWeek,
+              subtitle: l10n.planOptionWeekDesc,
+              onTap: () => _select(context, PlanMode.week),
+            ),
+          ],
+        ),
+      ),
+    );
+  }
+
+  void _select(BuildContext context, PlanMode mode) {
+    Navigator.pop(context);
+    onModeSelected(mode);
+  }
+}
+
+class _PlanOptionTile extends StatelessWidget {
+  const _PlanOptionTile({
+    required this.icon,
+    required this.title,
+    required this.subtitle,
+    required this.onTap,
+  });
+
+  final IconData icon;
+  final String title;
+  final String subtitle;
+  final VoidCallback onTap;
+
+  @override
+  Widget build(BuildContext context) {
+    final theme = Theme.of(context);
+    return Card(
+      margin: const EdgeInsets.only(bottom: 8),
+      child: ListTile(
+        leading: Icon(icon, color: theme.colorScheme.primary),
+        title: Text(title, style: theme.textTheme.titleSmall),
+        subtitle: Text(
+          subtitle,
+          style: theme.textTheme.bodySmall?.copyWith(
+            color: theme.colorScheme.onSurfaceVariant,
+          ),
+        ),
+        trailing: Icon(Icons.chevron_right,
+            color: theme.colorScheme.onSurfaceVariant),
+        onTap: onTap,
+      ),
+    );
+  }
+}