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

internal/server/routes_test.go

@@ -1178,12 +1178,12 @@ func TestHook_LinksBetweenPages(t *testing.T) {
 		// mobile menu link.
 		{
 			"/user/navigator/",
-			`href="([^"]+)" class="btn-text">Webhooks<`,
+			`href="([^"]+)" class="btn-secondary">Webhooks<`,
 			list,
 		},
 		{
 			"/user/navigator/",
-			`href="([^"]+)" class="btn-text w-full[^"]*">Webhooks<`,
+			`href="([^"]+)" class="btn-secondary w-full">Webhooks<`,
 			list,
 		},
 		{list, `href="(/hook/[^"]+)"`, page},