Make every clickable control look clickable, in two shared styles (closes #375)

Buttons keep btn-primary, btn-secondary and btn-danger and gain a
pointer cursor; the navigation links become btn-secondary buttons.
Every control that was plain coloured text (Copy, both Add, the row
actions, Resubmit, Replay, the back, footer and download links) now
uses btn-small, bordered at rest with hover and focus states. Both
styles are in static/css/style.css, which the layout now loads.

The event log's clickable rows become buttons, so they work by
keyboard; Replay moves beside its delivery's row. Rows on the webhook
page and in the event log wrap at phone width. The browser test now
checks that Copy reads "Copied".

Model: opus-5-5

templates/base.html

@@ -22,9 +22,9 @@
 <footer class="bg-gray-100 border-t border-gray-200 shadow-[0_-4px_6px_-1px_rgba(0,0,0,0.1)] mt-8">
     <div class="max-w-6xl mx-auto px-8 py-6">
         <div class="text-center text-sm text-gray-500 font-mono font-light">
-            <a href="https://git.eeqj.de/sneak/webhooker" class="hover:text-gray-700">Webhooker</a>
+            <a href="https://git.eeqj.de/sneak/webhooker" class="btn-small">Webhooker</a>
             <span class="mx-1">by</span>
-            <a href="https://sneak.berlin" class="hover:text-gray-700">@sneak</a>
+            <a href="https://sneak.berlin" class="btn-small">@sneak</a>
             <span class="mx-3">|</span>
             <span>{{if .Version}}{{.Version}}{{else}}dev{{end}}</span>
         </div>