Add Neon/Synthwave style and 4 paywall themes

- Add 4 distinct paywall themes (Celestial, Garden, Neon, Minimal) with
  preview/switcher in debug settings
- Add Neon voting layout with synthwave equalizer bar design
- Upgrade Neon entry style with grid background, cyan/magenta gradients,
  scanline effects, and mini equalizer visualization
- Add PaywallPreviewSettingsView for testing different paywall styles
- Use consistent synthwave color palette (cyan #00FFD0, magenta #FF00CC)

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Shared/Views/SettingsView/SettingsView.swift

@@ -54,6 +54,7 @@ struct SettingsContentView: View {
                 debugSectionHeader
                 trialDateButton
                 animationLabButton
+                paywallPreviewButton
                 #endif
 
                 Spacer()
@@ -245,6 +246,7 @@ struct SettingsContentView: View {
     }
 
     @State private var showAnimationLab = false
+    @State private var showPaywallPreview = false
 
     private var animationLabButton: some View {
         ZStack {
@@ -284,6 +286,51 @@ struct SettingsContentView: View {
             }
         }
     }
+
+    private var paywallPreviewButton: some View {
+        ZStack {
+            theme.currentTheme.secondaryBGColor
+            Button {
+                showPaywallPreview = true
+            } label: {
+                HStack(spacing: 12) {
+                    Image(systemName: "paintpalette.fill")
+                        .font(.title2)
+                        .foregroundStyle(
+                            LinearGradient(
+                                colors: [.purple, .pink, .orange],
+                                startPoint: .topLeading,
+                                endPoint: .bottomTrailing
+                            )
+                        )
+                        .frame(width: 32)
+
+                    VStack(alignment: .leading, spacing: 2) {
+                        Text("Paywall Styles")
+                            .foregroundColor(textColor)
+
+                        Text("Preview subscription themes")
+                            .font(.caption)
+                            .foregroundStyle(.secondary)
+                    }
+
+                    Spacer()
+
+                    Image(systemName: "chevron.right")
+                        .font(.caption)
+                        .foregroundStyle(.tertiary)
+                }
+                .padding()
+            }
+        }
+        .fixedSize(horizontal: false, vertical: true)
+        .cornerRadius(Constants.viewsCornerRaidus, corners: [.topLeft, .topRight, .bottomLeft, .bottomRight])
+        .sheet(isPresented: $showPaywallPreview) {
+            NavigationStack {
+                PaywallPreviewSettingsView()
+            }
+        }
+    }
     #endif
 
     // MARK: - Privacy Lock Toggle