fix(nav): add responsive hamburger menu for mobile

- Hide horizontal nav links below md breakpoint
- Add hamburger/close toggle button using Datastar signals
- Show vertical dropdown menu on mobile with stacked nav links

templates/nav.html

@@ -1,6 +1,8 @@
-<nav class="flex items-center justify-between gap-4 rounded-lg border border-amber-300 bg-amber-100/80 p-3 text-sm text-stone-600">
+<nav class="relative rounded-lg border border-amber-300 bg-amber-100/80 p-3 text-sm text-stone-600" data-signals:nav-open="false">
+    <div class="flex items-center justify-between">
         <div class="font-semibold uppercase tracking-[0.25em] text-amber-700"><a href="/timeline">B{rew}log</a></div>
-    <div class="flex items-center gap-3">
+        <!-- Desktop links -->
+        <div class="hidden md:flex items-center gap-3">
             <a class="border-b-2 pb-1 transition {% if nav_active == "roasters" %}text-amber-700 border-amber-500{% else %}text-stone-500 border-transparent hover:text-amber-600 hover:border-amber-400{% endif %}" href="/roasters">Roasters</a>
             <a class="border-b-2 pb-1 transition {% if nav_active == "roasts" %}text-amber-700 border-amber-500{% else %}text-stone-500 border-transparent hover:text-amber-600 hover:border-amber-400{% endif %}" href="/roasts">Roasts</a>
             <a class="border-b-2 pb-1 transition {% if nav_active == "bags" %}text-amber-700 border-amber-500{% else %}text-stone-500 border-transparent hover:text-amber-600 hover:border-amber-400{% endif %}" href="/bags">Bags</a>
@@ -15,4 +17,30 @@
             <a class="border-b-2 pb-1 transition text-stone-500 border-transparent hover:text-amber-600 hover:border-amber-400" href="/login">Login</a>
             {% endif %}
         </div>
+        <!-- Hamburger button (mobile only) -->
+        <button class="md:hidden p-1 text-amber-700" data-on:click="$navOpen = !$navOpen" aria-label="Toggle menu">
+            <svg data-show="!$navOpen" class="h-6 w-6" fill="none" viewBox="0 0 24 24" stroke="currentColor" stroke-width="2">
+                <path stroke-linecap="round" stroke-linejoin="round" d="M4 6h16M4 12h16M4 18h16" />
+            </svg>
+            <svg data-show="$navOpen" class="h-6 w-6" fill="none" viewBox="0 0 24 24" stroke="currentColor" stroke-width="2" style="display:none">
+                <path stroke-linecap="round" stroke-linejoin="round" d="M6 18L18 6M6 6l12 12" />
+            </svg>
+        </button>
+    </div>
+    <!-- Mobile menu -->
+    <div class="md:hidden flex flex-col gap-2 pt-3 mt-3 border-t border-amber-300" data-show="$navOpen" style="display:none">
+        <a class="py-1 transition {% if nav_active == "roasters" %}text-amber-700 font-medium{% else %}text-stone-500 hover:text-amber-600{% endif %}" href="/roasters">Roasters</a>
+        <a class="py-1 transition {% if nav_active == "roasts" %}text-amber-700 font-medium{% else %}text-stone-500 hover:text-amber-600{% endif %}" href="/roasts">Roasts</a>
+        <a class="py-1 transition {% if nav_active == "bags" %}text-amber-700 font-medium{% else %}text-stone-500 hover:text-amber-600{% endif %}" href="/bags">Bags</a>
+        <a class="py-1 transition {% if nav_active == "brews" %}text-amber-700 font-medium{% else %}text-stone-500 hover:text-amber-600{% endif %}" href="/brews">Brews</a>
+        <a class="py-1 transition {% if nav_active == "gear" %}text-amber-700 font-medium{% else %}text-stone-500 hover:text-amber-600{% endif %}" href="/gear">Gear</a>
+        <a class="py-1 transition {% if nav_active == "timeline" %}text-amber-700 font-medium{% else %}text-stone-500 hover:text-amber-600{% endif %}" href="/timeline">Timeline</a>
+        {% if is_authenticated %}
+        <form method="post" action="/logout" class="inline">
+            <button type="submit" class="py-1 transition text-stone-500 hover:text-amber-600 text-left">Logout</button>
+        </form>
+        {% else %}
+        <a class="py-1 transition text-stone-500 hover:text-amber-600" href="/login">Login</a>
+        {% endif %}
+    </div>
 </nav>