Complete accessibility identifier coverage across all 152 project files

Exhaustive file-by-file audit of every Swift file in the project (iOS app,
Watch app, Widget extension). Every interactive UI element — buttons, toggles,
pickers, links, menus, tap gestures, text editors, color pickers, photo
pickers — now has an accessibilityIdentifier for XCUITest automation.

46 files changed across Shared/, Onboarding/, Watch App/, and Widget targets.
Added ~100 new ID definitions covering settings debug controls, export/photo
views, sharing templates, customization subviews, onboarding flows, tip
modals, widget voting buttons, and watch mood buttons.

Shared/Views/CustomizeView/SubViews/ThemePickerView.swift

@@ -58,6 +58,7 @@ struct ThemePickerView: View {
                 .fill(selectedTheme == theme ? selectedTheme.currentTheme.bgColor : .clear)
                 .padding(-5)
         )
+        .accessibilityIdentifier(AccessibilityID.Customize.themeButton(theme.title))
     }
 
     private func selectTheme(_ theme: Theme) {