feat: unified food calendar — extend home screen to future dates + planned meals

Phase 1: date strip now covers today + 7 future days; right chevron enabled;
future pills rendered in lighter style.

Phase 2: home screen shows DateContext (past/today/future):
- future dates: hide calorie ring + macros, show PlanningBanner
- plannedMealsProvider derives from cached menuProvider (no extra API call)
- _MealCard shows ghost PlannedSlotTile for unconfirmed menu slots
- "Mark as eaten" creates a diary entry (source: menu_plan) via existing API

New l10n keys (12 locales): planningForDate, markAsEaten, plannedMealLabel

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

client/lib/l10n/app_localizations_it.dart

@@ -350,4 +350,15 @@ class AppLocalizationsIt extends AppLocalizations {
 
   @override
   String get scanDishPhoto => 'Scansiona foto';
+
+  @override
+  String planningForDate(String date) {
+    return '';
+  }
+
+  @override
+  String get markAsEaten => '';
+
+  @override
+  String get plannedMealLabel => '';
 }