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/tailwind.config.js

@@ -0,0 +1,22 @@
+/** @type {import('tailwindcss').Config} */
+export default {
+  content: ['./index.html', './src/**/*.{js,ts,jsx,tsx}'],
+  theme: {
+    extend: {
+      colors: {
+        brand: {
+          50:  '#eff6ff',
+          100: '#dbeafe',
+          500: '#3b82f6',
+          600: '#2563eb',
+          700: '#1d4ed8',
+          900: '#1e3a5f',
+        },
+      },
+      fontFamily: {
+        sans: ['Inter', 'system-ui', 'sans-serif'],
+      },
+    },
+  },
+  plugins: [],
+};