Add shared site header with account dropdown

Add SiteHeader and AccountDropdown components, replace
inline headers across homepage, roadmap, and docs layout.

app/page.tsx

@@ -1,5 +1,4 @@
-import Link from "next/link";
-import { Globe, Search, Shield, Activity } from "lucide-react";
+import { Search, Shield, Activity } from "lucide-react";
 import {
   Card,
   CardHeader,
@@ -7,7 +6,7 @@ import {
   CardDescription,
 } from "@/components/ui/card";
 import { Badge } from "@/components/ui/badge";
-import { ThemeToggle } from "@/components/theme-toggle";
+import { SiteHeader } from "@/components/site-header";
 import { DomainSearchForm } from "@/components/domain-search-form";
 
 const features = [
@@ -34,38 +33,13 @@ const features = [
 export default function Home() {
   return (
     <div className="flex min-h-screen flex-col">
-      {/* Header */}
-      <header className="border-b">
-        <div className="container mx-auto flex h-14 items-center justify-between px-4">
-          <div className="flex items-center gap-2">
-            <Globe className="size-5 text-primary" />
-            <span className="text-lg font-semibold tracking-tight">
-              VectorDNS
-            </span>
-          </div>
-          <div className="flex items-center gap-4">
-            <Link
-              href="/docs"
-              className="text-sm text-muted-foreground transition-colors hover:text-foreground"
-            >
-              Docs
-            </Link>
-            <Link
-              href="/roadmap"
-              className="text-sm text-muted-foreground transition-colors hover:text-foreground"
-            >
-              Roadmap
-            </Link>
-            <ThemeToggle />
-          </div>
-        </div>
-      </header>
+      <SiteHeader />
 
       {/* Hero */}
       <main className="flex flex-1 flex-col">
         <section className="flex flex-col items-center justify-center gap-6 px-4 py-24 text-center md:py-32">
           <Badge variant="secondary" className="text-sm">
-            Free DNS Toolkit
+            Total DNS Toolkit
           </Badge>
           <h1 className="max-w-2xl text-4xl font-bold tracking-tight sm:text-5xl">
             DNS Lookup, WHOIS &amp;{" "}