feat(web): add Property Valuation UI with AVM integration

Build the valuation page at /dashboard/valuation with form input,
AI-powered price estimation results, comparable properties display,
and valuation history. Add "Dinh gia AI" button to listing detail
sidebar for quick per-listing estimates.

Co-Authored-By: Paperclip <noreply@paperclip.ing>

apps/web/app/(dashboard)/layout.tsx

@@ -12,6 +12,7 @@ const navItems = [
   { href: '/listings', label: 'Tin đăng', icon: '📋' },
   { href: '/listings/new', label: 'Đăng tin', icon: '➕' },
   { href: '/analytics', label: 'Phân tích', icon: '📊' },
+  { href: '/dashboard/valuation', label: 'Định giá AI', icon: '🤖' },
   { href: '/dashboard/profile', label: 'Hồ sơ', icon: '👤' },
   { href: '/dashboard/subscription', label: 'Gói dịch vụ', icon: '💎' },
   { href: '/dashboard/payments', label: 'Thanh toán', icon: '💳' },