feat: replace ghost buttons with underline tab bar for site navigation

Dashboard, Uptime, Funnels, and Settings now use a consistent
underline tab bar with orange active indicator, matching the
existing panel tab design language.

components/dashboard/SiteNav.tsx

@@ -0,0 +1,54 @@
+'use client'
+
+import Link from 'next/link'
+import { usePathname } from 'next/navigation'
+import { useTabListKeyboard } from '@/lib/hooks/useTabListKeyboard'
+import { useAuth } from '@/lib/auth/context'
+
+interface SiteNavProps {
+  siteId: string
+}
+
+export default function SiteNav({ siteId }: SiteNavProps) {
+  const pathname = usePathname()
+  const handleTabKeyDown = useTabListKeyboard()
+  const { user } = useAuth()
+  const canEdit = user?.role === 'owner' || user?.role === 'admin'
+
+  const tabs = [
+    { label: 'Dashboard', href: `/sites/${siteId}` },
+    { label: 'Uptime', href: `/sites/${siteId}/uptime` },
+    { label: 'Funnels', href: `/sites/${siteId}/funnels` },
+    ...(canEdit ? [{ label: 'Settings', href: `/sites/${siteId}/settings` }] : []),
+  ]
+
+  const isActive = (href: string) => {
+    if (href === `/sites/${siteId}`) {
+      return pathname === href || pathname === `${href}/realtime`
+    }
+    return pathname.startsWith(href)
+  }
+
+  return (
+    <div className="border-b border-neutral-200 dark:border-neutral-800 mb-6">
+      <nav className="flex gap-1" role="tablist" aria-label="Site navigation" onKeyDown={handleTabKeyDown}>
+        {tabs.map((tab) => (
+          <Link
+            key={tab.href}
+            href={tab.href}
+            role="tab"
+            aria-selected={isActive(tab.href)}
+            tabIndex={isActive(tab.href) ? 0 : -1}
+            className={`px-3 py-2 text-sm font-medium transition-colors focus:outline-none focus:ring-2 focus:ring-brand-orange rounded-t cursor-pointer border-b-2 -mb-px ${
+              isActive(tab.href)
+                ? 'border-brand-orange text-neutral-900 dark:text-white'
+                : 'border-transparent text-neutral-400 dark:text-neutral-500 hover:text-neutral-700 dark:hover:text-neutral-300'
+            }`}
+          >
+            {tab.label}
+          </Link>
+        ))}
+      </nav>
+    </div>
+  )
+}