Update Neon colors and show color circles in theme picker

- Update NeonMoodTint to use synthwave colors matching Neon voting style
  (cyan, lime, yellow, orange, magenta)
- Replace text label with 5 color circles in theme preview Colors row
- Remove unused textColor customization code and picker views
- Add .id(moodTint) to Month/Year views for color refresh
- Clean up various unused color-related code

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

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

Shared/Models/Theme.swift

@@ -43,7 +43,7 @@ enum Theme: String, CaseIterable {
     
     var currentTheme: Themeable {
         switch self {
-            
+
         case .system:
             return SystemTheme()
         case .iFeel:
@@ -54,6 +54,17 @@ enum Theme: String, CaseIterable {
             return AlwaysLight()
         }
     }
+
+    var preferredColorScheme: ColorScheme? {
+        switch self {
+        case .system, .iFeel:
+            return nil // Follow system
+        case .dark:
+            return .dark
+        case .light:
+            return .light
+        }
+    }
 }
 
 protocol Themeable {