feat: add admin panel

src/beaver_gateway/frontends/admin/templates/_token_created.html

@@ -0,0 +1,12 @@
+{# Renders into #token-create-result (hx-target on the form). The
+   two OOB swaps reach the rest of the page: prepend the new row,
+   and erase the empty-state placeholder if it's still in the DOM. #}
+<div class="banner warn">
+  <strong>Token created: {{ token.name }}</strong>
+  <p class="muted" style="margin:0.25rem 0 0.5rem;">Copy it now — this is the only time it will be shown.</p>
+  <pre style="margin:0;">{{ plaintext }}</pre>
+</div>
+<tbody id="tokens-rows" hx-swap-oob="afterbegin">
+  {% include "_token_row.html" %}
+</tbody>
+<tr id="tokens-empty" hx-swap-oob="delete"></tr>