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

static/css/style.css

@@ -1 +1,48 @@
-/* Webhooker custom styles — see input.css for Tailwind theme */
+/*
+ * The two shared styles for the controls a user clicks. Every page loads
+ * this file after tailwind.css. It is plain CSS: make css does not build
+ * it.
+ *
+ * A button is btn-primary, btn-secondary or btn-danger, from input.css.
+ * A secondary or inline action, such as Copy beside an entrypoint URL or
+ * Edit beside a target, is btn-small.
+ *
+ * Each card on the webhook list is a card-elevated link as a whole. It
+ * shows an Open label in btn-small and takes btn-small's focus outline.
+ *
+ * The rules join tailwind.css's components layer, where input.css puts
+ * its own, so a utility class on an element still overrides them.
+ */
+@layer components {
+    /* input.css gives its buttons no pointer cursor. */
+    .btn-primary,
+    .btn-secondary,
+    .btn-danger {
+        cursor: pointer;
+    }
+
+    .btn-small {
+        display: inline-flex;
+        align-items: center;
+        padding: 0.25rem 0.625rem;
+        border: 1px solid var(--color-gray-300);
+        border-radius: var(--radius-md);
+        background-color: var(--color-white);
+        color: var(--color-primary-700);
+        font-size: var(--text-xs);
+        line-height: 1rem;
+        font-weight: var(--font-weight-medium);
+        cursor: pointer;
+    }
+
+    .btn-small:hover {
+        border-color: var(--color-primary-500);
+        background-color: var(--color-primary-50);
+    }
+
+    .btn-small:focus-visible,
+    .card-elevated:focus-visible {
+        outline: 2px solid var(--color-primary-500);
+        outline-offset: 2px;
+    }
+}