fix(spa): complete checkout flow, UI standardization, and tailwind v4 styling fixes

apps/spa/src/index.css

@@ -11,6 +11,13 @@
   --color-pop-bg: #FFF0F5;
   --color-pop-black: #333333;
 
+  /* Spa Theme Colors */
+  --color-spa-light: #FDFDF9;
+  --color-spa-sage: #EAEFEA;
+  --color-spa-stone: #4B4B46;
+  --color-spa-forest: #1F3D2D;
+  --color-spa-gold: #D4AF37;
+
   --shadow-brutal: 0 10px 25px rgba(0,0,0,0.05);
   --shadow-brutal-hover: 0 20px 40px rgba(0,0,0,0.1);