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 site name and 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. Each card on the webhook list shows an Open label in
btn-small and takes its focus outline. 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/sources_list.html

@@ -25,7 +25,12 @@
                     <p class="text-sm text-gray-500 mt-1">{{.Description}}</p>
                     {{end}}
                 </div>
-                <span class="badge-info">Retention: {{.RetentionLabel}}</span>
+                <div class="flex flex-wrap items-center gap-2">
+                    <span class="badge-info">Retention: {{.RetentionLabel}}</span>
+                    <!-- A label, not a control of its own: the whole card
+                         is the link. -->
+                    <span class="btn-small">Open &rarr;</span>
+                </div>
             </div>
             <div class="flex flex-wrap gap-6 mt-4 text-sm text-gray-500">
                 <span>{{.EntrypointCount}} entrypoint{{if ne .EntrypointCount 1}}s{{end}}{{if .InactiveEntrypointCount}}, {{.InactiveEntrypointCount}} inactive{{end}}</span>