feat(inquiries): top-level Inquiries page (list + detail + convert), nav entries; retire admin inbox

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

src/components/layout/sidebar.tsx

@@ -16,6 +16,7 @@ import {
   FileText,
   FileBarChart,
   Inbox,
+  MailQuestion,
   Camera,
   Globe,
   Settings,
@@ -115,6 +116,7 @@ function buildNavSections(portSlug: string | undefined): NavSection[] {
         { href: `${base}/yachts`, label: 'Yachts', icon: Ship },
         { href: `${base}/companies`, label: 'Companies', icon: Building2 },
         { href: `${base}/interests`, label: 'Interests', icon: Bookmark },
+        { href: `${base}/inquiries`, label: 'Inquiries', icon: MailQuestion },
         { href: `${base}/berths`, label: 'Berths', icon: Anchor },
         {
           href: `${base}/tenancies`,