feat: initial website commit + installation guide page

- Full nixpanel-website monorepo: web (React/Vite) + api (Fastify)
- Add /install page with one-liner, manual steps, requirements,
  software table, firewall ports, service management, and update/uninstall
- Add Install link to header nav and footer
- Add 'Install guide' CTA button to home page hero
- Add 'outline' variant to Button component
- Add .gitignore and .gitattributes

Co-Authored-By: Claude Sonnet 4.6 <[email protected]>

web/index.html

@@ -0,0 +1,16 @@
+<!doctype html>
+<html lang="en">
+  <head>
+    <meta charset="UTF-8" />
+    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
+    <meta name="description" content="NixPanel — The open hosting control panel. Manage your servers with confidence." />
+    <link rel="preconnect" href="https://fonts.googleapis.com" />
+    <link rel="preconnect" href="https://fonts.gstatic.com" crossorigin />
+    <link href="https://fonts.googleapis.com/css2?family=Inter:wght@400;500;600;700;800&display=swap" rel="stylesheet" />
+    <title>NixPanel — Hosting Control Panel</title>
+  </head>
+  <body>
+    <div id="root"></div>
+    <script type="module" src="/src/main.tsx"></script>
+  </body>
+</html>