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/Models/UserDefaultsStore.swift

@@ -14,6 +14,7 @@ enum VotingLayoutStyle: Int, CaseIterable {
     case stacked = 3      // Full-width vertical list
     case aura = 4         // Atmospheric glowing orbs with flowing layout
     case orbit = 5        // Celestial orbit with center core
+    case neon = 6         // Synthwave arcade equalizer with glowing segments
 
     var displayName: String {
         switch self {
@@ -23,6 +24,32 @@ enum VotingLayoutStyle: Int, CaseIterable {
         case .stacked: return "Stacked"
         case .aura: return "Aura"
         case .orbit: return "Orbit"
+        case .neon: return "Neon"
+        }
+    }
+}
+
+enum PaywallStyle: Int, CaseIterable {
+    case celestial = 0    // Celestial Self-Discovery - aurora, floating orbs
+    case garden = 1       // Garden Growth - organic, blooming nature
+    case neon = 2         // Neon Pulse - synthwave, energetic
+    case minimal = 3      // Minimal Zen - clean, sophisticated
+
+    var displayName: String {
+        switch self {
+        case .celestial: return "Celestial"
+        case .garden: return "Garden"
+        case .neon: return "Neon"
+        case .minimal: return "Minimal"
+        }
+    }
+
+    var description: String {
+        switch self {
+        case .celestial: return "Aurora lights & floating emotion orbs"
+        case .garden: return "Blooming flowers & organic growth"
+        case .neon: return "Synthwave energy & glowing pulses"
+        case .minimal: return "Clean typography & subtle elegance"
         }
     }
 }
@@ -105,6 +132,7 @@ class UserDefaultsStore {
         case privacyLockEnabled
         case healthKitEnabled
         case healthKitSyncEnabled
+        case paywallStyle
 
         case contentViewCurrentSelectedHeaderViewBackDays
         case contentViewHeaderTag