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>

Tests iOS/Helpers/WaitHelpers.swift

@@ -82,6 +82,14 @@ enum UITestID {
         static let header = "insights_header"
     }
 
+    enum Year {
+        static let donutChart = "year_donut_chart"
+        static let barChart = "year_bar_chart"
+        static let statsSection = "year_stats_section"
+        static func cardHeader(year: Int) -> String { "year_card_header_\(year)" }
+        static let shareButton = "year_share_button"
+    }
+
     enum Month {
         static let grid = "month_grid"
     }