1.2.1: surface "Copy previous week" on the empty-week banner

The exact-copy-from-previous-week action already existed but was buried in the
magic-wand long-press context menu. Expose it as a visible secondary button on
the auto-assign banner (shown only when the previous week actually has a menu),
so users landing on a fresh week can one-tap copy last week's plan and then tweak
it. Confirms before overwriting a week that already has dishes.

- Extract requestCopyPreviousWeek() shared by the menu and the banner.
- Add week_copied_previous analytics (copied_slots + source: empty_banner|menu).
- Reuses the existing localized home_copy_previous_week string (all 6 languages).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01BkanrydYtrme8wipTzWssG

MealMood/Services/AnalyticsService.swift

@@ -21,6 +21,7 @@ enum AnalyticsEvent {
 
     // Planner
     static let autoAssignUsed = "auto_assign_used"
+    static let weekCopiedPrevious = "week_copied_previous"
 
     // Onboarding
     static let onboardingStepViewed = "onboarding_step_viewed"
@@ -112,6 +113,13 @@ enum AnalyticsService {
         ])
     }
 
+    static func logWeekCopiedPrevious(copiedSlots: Int, source: String) {
+        logEvent(AnalyticsEvent.weekCopiedPrevious, parameters: [
+            "copied_slots": copiedSlots,
+            "source": source
+        ])
+    }
+
     static func logICloudSyncToggled(enabled: Bool) {
         logEvent(AnalyticsEvent.iCloudSyncToggled, parameters: ["enabled": enabled])
     }