feat: add model plaza with group-scoped pricing showcase

- public /model-plaza page (standalone + admin-embedded) listing groups
  with discounted effective prices alongside LiteLLM official reference
- faceted platform/group/rate filters: cross-dimension options gray out
  instead of disappearing, platform-tinted chips via accent color-mix
- paid-price columns highlighted with per-platform tint band
- OptionalJWT middleware so anonymous and signed-in users share one route
- admin settings: enable switch, require-auth switch, markdown description

frontend/src/utils/featureFlags.ts

@@ -104,6 +104,11 @@ export const FeatureFlags = {
     mode: 'opt-in',
     label: 'Available Channels',
   }),
+  modelPlaza: defineFlag({
+    key: 'model_plaza_enabled',
+    mode: 'opt-in',
+    label: 'Model Plaza',
+  }),
   payment: defineFlag({
     key: 'payment_enabled',
     mode: 'opt-out',

frontend/src/utils/platformColors.ts

@@ -39,6 +39,29 @@ const BORDER: Record<Platform, string> = {
 }
 const BORDER_DEFAULT = 'border-gray-200 dark:border-dark-700'
 
+// ── Border strong (higher-contrast platform tint, e.g. plaza group cards) ──
+const BORDER_STRONG: Record<Platform, string> = {
+  anthropic: 'border-orange-500/35 dark:border-orange-500/30',
+  openai: 'border-green-500/35 dark:border-green-500/30',
+  antigravity: 'border-purple-500/35 dark:border-purple-500/30',
+  gemini: 'border-blue-500/35 dark:border-blue-500/30',
+  grok: 'border-zinc-800/35 dark:border-zinc-500/35',
+  composite: 'border-cyan-500/35 dark:border-cyan-500/30',
+}
+const BORDER_STRONG_DEFAULT = 'border-gray-300 dark:border-dark-600'
+
+// ── Accent (single raw color per platform; consumers derive washes/tints
+//    from it via CSS color-mix, e.g. plaza paid-price zone) ──
+const ACCENT: Record<Platform, string> = {
+  anthropic: '#f97316', // orange-500
+  openai: '#22c55e', // green-500
+  antigravity: '#a855f7', // purple-500
+  gemini: '#3b82f6', // blue-500
+  grok: '#71717a', // zinc-500
+  composite: '#06b6d4', // cyan-500
+}
+const ACCENT_DEFAULT = '#14b8a6' // primary-500 (teal)
+
 // ── Accent bar (gradient) ───────────────────────────────────────────
 const ACCENT_BAR: Record<Platform, string> = {
   anthropic: 'bg-gradient-to-r from-orange-400 to-orange-500',
@@ -144,6 +167,14 @@ export function platformBorderClass(p: string): string {
   return isPlatform(p) ? BORDER[p] : BORDER_DEFAULT
 }
 
+export function platformBorderStrongClass(p: string): string {
+  return isPlatform(p) ? BORDER_STRONG[p] : BORDER_STRONG_DEFAULT
+}
+
+export function platformAccentColor(p: string): string {
+  return isPlatform(p) ? ACCENT[p] : ACCENT_DEFAULT
+}
+
 export function platformAccentBarClass(p: string): string {
   return isPlatform(p) ? ACCENT_BAR[p] : ACCENT_BAR_DEFAULT
 }

frontend/src/utils/pricing.ts

@@ -1,13 +1,24 @@
 /**
  * formatScaled formats a per-token (or per-request) USD price scaled by `scale`.
  *
- *   formatScaled(0.000003, 1_000_000) → "$3"        // per 1M tokens
- *   formatScaled(0.5,        1)        → "$0.5"      // per request
- *   formatScaled(null,       1_000_000) → "-"
+ *   formatScaled(0.000003, 1_000_000)    → "$3"      // per 1M tokens
+ *   formatScaled(0.5,        1)          → "$0.5"    // per request
+ *   formatScaled(null,       1_000_000)  → "-"
+ *   formatScaled(0.000003, 1_000_000, 2) → "$3.00"   // pad to ≥2 decimals
+ *   formatScaled(1.25e-8,  1_000_000, 2) → "$0.0125" // longer decimals kept as-is
  *
  * Uses toPrecision(10) then strips trailing zeros to avoid IEEE 754 display noise.
+ * `minFractionDigits` pads the result back up to a minimum number of decimals.
  */
-export function formatScaled(value: number | null, scale: number): string {
+export function formatScaled(value: number | null, scale: number, minFractionDigits = 0): string {
   if (value == null) return '-'
-  return `$${(value * scale).toPrecision(10).replace(/\.?0+$/, '')}`
+  let s = (value * scale).toPrecision(10).replace(/\.?0+$/, '')
+  if (minFractionDigits > 0 && !s.includes('e')) {
+    const dot = s.indexOf('.')
+    const digits = dot === -1 ? 0 : s.length - dot - 1
+    if (digits < minFractionDigits) {
+      s = (dot === -1 ? `${s}.` : s) + '0'.repeat(minFractionDigits - digits)
+    }
+  }
+  return `$${s}`
 }