feat(ui): responsive layout for mobile and wide screens

- Add explicit viewport meta (device-width) for proper mobile scaling.
- Widen the main container (720 -> 960, 1120 on >=1280px) with fluid
  clamp() padding so wide screens are used better.
- Wrap the top nav and allow it to reflow on narrow screens.
- Collapse the key/value grid to a single column and enlarge touch
  targets on small screens.
- Keep single-form pages (login/signup/activate) in a readable narrow
  column instead of stretching full width.

app/activate/page.tsx

@@ -24,7 +24,7 @@ export default async function ActivatePage({
     .maybeSingle<{ subdomain: string }>();
 
   return (
-    <div>
+    <div className="form-card">
       <h1>Activate device</h1>
       <p className="muted">
         Enter the code shown by your Home Assistant add-on to pair it with your

app/globals.css

@@ -40,9 +40,22 @@ a:hover {
 }
 
 .container {
-  max-width: 720px;
+  width: 100%;
+  max-width: 960px;
   margin: 0 auto;
-  padding: 2rem 1rem;
+  padding: 2rem clamp(1rem, 4vw, 2.5rem);
+}
+
+/* Narrow column for single-form pages (login/signup/activate) that read
+   better when not stretched across a wide screen. */
+.container.narrow {
+  max-width: 480px;
+}
+
+@media (min-width: 1280px) {
+  .container {
+    max-width: 1120px;
+  }
 }
 
 .stack {
@@ -55,7 +68,9 @@ a:hover {
   display: flex;
   justify-content: space-between;
   align-items: center;
-  padding: 1rem;
+  gap: 0.75rem 1rem;
+  flex-wrap: wrap;
+  padding: 0.85rem clamp(1rem, 4vw, 2.5rem);
   border-bottom: 1px solid var(--border);
 }
 
@@ -67,6 +82,14 @@ a:hover {
   margin: 1rem 0;
 }
 
+/* Single-form cards (login / signup / activate) stay readable instead of
+   stretching across a wide screen. */
+.form-card {
+  max-width: 460px;
+  margin-left: auto;
+  margin-right: auto;
+}
+
 h1,
 h2,
 h3 {
@@ -170,6 +193,36 @@ button.secondary,
   display: flex;
   gap: 0.5rem;
   align-items: center;
+  flex-wrap: wrap;
+}
+
+/* ----------------------------------------------------------------------- */
+/* Mobile / small-screen refinements                                        */
+/* ----------------------------------------------------------------------- */
+@media (max-width: 520px) {
+  .kv {
+    grid-template-columns: 1fr;
+    gap: 0.15rem 0;
+  }
+  .kv .k {
+    margin-top: 0.5rem;
+  }
+  .card {
+    padding: 1.15rem;
+  }
+  /* Larger touch targets on touch devices. */
+  button,
+  .btn,
+  input[type='text'],
+  input[type='email'],
+  input[type='password'],
+  select {
+    min-height: 44px;
+  }
+  .nav button,
+  .nav .btn {
+    padding: 0.5rem 0.8rem;
+  }
 }
 
 /* ----------------------------------------------------------------------- */

app/layout.tsx

@@ -1,4 +1,4 @@
-import type { Metadata } from 'next';
+import type { Metadata, Viewport } from 'next';
 import Link from 'next/link';
 import './globals.css';
 import { createSupabaseServerClient } from '@/lib/supabase/server';
@@ -8,6 +8,11 @@ export const metadata: Metadata = {
   description: 'Remote access tunnels for Home Assistant',
 };
 
+export const viewport: Viewport = {
+  width: 'device-width',
+  initialScale: 1,
+};
+
 export const dynamic = 'force-dynamic';
 
 export default async function RootLayout({

app/login/page.tsx

@@ -85,7 +85,7 @@ export default function LoginPage() {
   }
 
   return (
-    <div className="card">
+    <div className="card form-card">
       <h1>Login</h1>
       <form onSubmit={onSubmit}>
         <label htmlFor="email">Email</label>

app/signup/page.tsx

@@ -77,7 +77,7 @@ export default function SignupPage() {
 
   if (submitted) {
     return (
-      <div className="card">
+      <div className="card form-card">
         <h1>Check your email</h1>
         <p>
           We sent a confirmation link to <strong>{email}</strong>. Click the
@@ -106,7 +106,7 @@ export default function SignupPage() {
   }
 
   return (
-    <div className="card">
+    <div className="card form-card">
       <h1>Sign up</h1>
       <form onSubmit={onSubmit}>
         <label htmlFor="email">Email</label>