Refactor ZStack layouts to .background(), add Year View accessibility IDs, triage QA test plan

Replace ZStack-with-gradient patterns with idiomatic .background() modifier
across onboarding, customize, and settings views. Add accessibility identifiers
to Year View charts for UI test automation. Mark 67 impossible-to-automate
tests RED in QA plan and scaffold initial Year View and Settings onboarding tests.

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

Shared/Views/AddMoodHeaderView.swift

@@ -41,8 +41,6 @@ struct AddMoodHeaderView: View {
             Text(String(imagePack.rawValue))
                 .hidden()
 
-            theme.currentTheme.secondaryBGColor
-
             VStack(spacing: 16) {
                 Text(ShowBasedOnVoteLogics.getVotingTitle(onboardingData: onboardingData))
                     .font(.title2.bold())
@@ -66,6 +64,7 @@ struct AddMoodHeaderView: View {
                 }
             }
         }
+        .background(theme.currentTheme.secondaryBGColor)
         .cornerRadius(Constants.viewsCornerRaidus, corners: [.topLeft, .topRight, .bottomLeft, .bottomRight])
         .fixedSize(horizontal: false, vertical: true)
         .accessibilityIdentifier(AccessibilityID.DayView.moodHeader)