style(css): add design tokens (primary-rgb, warning, spacing, shadow, tabular-nums)

src/main/resources/static/css/variables.css

@@ -29,6 +29,25 @@
     --radius-lg: 20px;
     --radius-full: 9999px;
 
+    /* Semantic (added) */
+    --warning: #f59e0b;
+    --primary-rgb: 59, 130, 246;   /* matches --primary #3b82f6; used by rgba(var(--primary-rgb), …) */
+    --success-rgb: 16, 185, 129;
+    --danger-rgb: 239, 68, 68;
+
+    /* Spacing scale */
+    --space-1: 0.25rem;
+    --space-2: 0.5rem;
+    --space-3: 0.75rem;
+    --space-4: 1rem;
+    --space-6: 1.5rem;
+    --space-8: 2rem;
+
+    /* Elevation */
+    --shadow-sm: 0 1px 2px rgba(0, 0, 0, 0.2);
+    --shadow-md: 0 4px 12px -2px rgba(0, 0, 0, 0.3);
+    --shadow-lg: 0 20px 25px -5px rgba(0, 0, 0, 0.35);
+
     --font-sans: 'Inter', -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, sans-serif;
 }
 
@@ -39,6 +58,7 @@ body {
     background-attachment: fixed;
     color: var(--text-primary);
     font-family: var(--font-sans);
+    font-feature-settings: "tnum" 1, "cv01" 1;
     margin: 0;
     -webkit-font-smoothing: antialiased;
     min-height: 100vh;