Load Alpine's CSP build so the UI's directives run (closes #371)

The pages' Content-Security-Policy forbids eval, which the standard
Alpine.js build needs, so no directive ran: add forms showed open and
events never collapsed. 3p/ now holds the @alpinejs/csp 3.14.9 tarball
instead, and every directive in templates/ names a property or method
of a component registered in static/js/app.js, as that build requires.
The policy is unchanged.

A headless Chromium test in internal/server loads the webhook page and
the event log under the real headers. The Dockerfile's test stage
installs chromium; where it is missing the test skips.

Model: opus-5-5

templates/navbar.html

@@ -1,14 +1,14 @@
 {{define "navbar"}}
-<nav class="app-bar" x-data="{ open: false }">
+<nav class="app-bar" x-data="collapsible">
     <div class="max-w-6xl mx-auto flex justify-between items-center">
         <div class="flex items-center gap-3">
             <a href="/" class="text-xl font-medium text-gray-900 hover:text-primary-600 transition-colors">Webhooker</a>
         </div>
 
         <!-- Mobile menu button -->
-        <button @click="open = !open" class="md:hidden p-2 rounded-md text-gray-500 hover:bg-gray-100">
+        <button @click="toggle" class="md:hidden p-2 rounded-md text-gray-500 hover:bg-gray-100">
             <svg class="w-6 h-6" fill="none" stroke="currentColor" viewBox="0 0 24 24">
-                <path x-show="!open" stroke-linecap="round" stroke-linejoin="round" stroke-width="2" d="M4 6h16M4 12h16M4 18h16"/>
+                <path x-show="closed" stroke-linecap="round" stroke-linejoin="round" stroke-width="2" d="M4 6h16M4 12h16M4 18h16"/>
                 <path x-show="open" x-cloak stroke-linecap="round" stroke-linejoin="round" stroke-width="2" d="M6 18L18 6M6 6l12 12"/>
             </svg>
         </button>