feat(pricing): add PricingView + calculator with bilingual i18n

Port Pricing.html verbatim to Vue: hero with preview pill, 4-tier grid,
custom-amount slider, PricingCalculator subcomponent, works-everywhere
grid, FAQ accordions, final CTA. Full zh/en pricing namespace (~200 keys
each). SOON chip on Scale priority feature; zero-log FAQ uses inline
parenthetical. Drop $5 bonus line; Enterprise → mailto, Binding/tiers →
/register, docs link → /register/docs.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

frontend/src/router/index.ts

@@ -129,6 +129,12 @@ const routes: RouteRecordRaw[] = [
       title: 'PURO AI · 文档'
     }
   },
+  {
+    path: '/pricing',
+    name: 'pricing',
+    component: () => import('@/views/pricing/PricingView.vue'),
+    meta: { requiresAuth: false, title: 'Pricing · PURO AI' }
+  },
 
   // ==================== User Routes ====================
   {