feat(webui): add central icon button

webui/tests/icon-button.test.tsx

@@ -0,0 +1,40 @@
+function assert(condition: unknown, message = "assertion failed"): void {
+  if (!condition) throw new Error(message);
+}
+
+import { renderToStaticMarkup } from "react-dom/server";
+import AdminIconButton from "../src/components/admin/AdminIconButton";
+import IconButton from "../src/components/IconButton";
+import { PlatformLanguageProvider } from "../src/i18n/LanguageContext";
+
+function noop() {}
+
+const iconButtonMarkup = renderToStaticMarkup(
+  <PlatformLanguageProvider>
+    <IconButton
+      label="i18n:govoplan-core.remove.e963907d"
+      icon={<svg><path /></svg>}
+      variant="danger"
+      className="context-action"
+      onClick={noop}
+    />
+  </PlatformLanguageProvider>
+);
+assert(iconButtonMarkup.includes('type="button"'), "icon buttons default to a non-submitting button");
+assert(iconButtonMarkup.includes('class="btn btn-danger icon-button context-action"'), "central variants and caller classes are preserved");
+assert(iconButtonMarkup.includes('aria-label="Remove"'), "the accessible label is translated");
+assert(iconButtonMarkup.includes('title="Remove"'), "the native title is translated");
+assert(iconButtonMarkup.includes('class="icon-button-icon" aria-hidden="true"'), "the visible icon is decorative");
+
+const reasonedMarkup = renderToStaticMarkup(
+  <IconButton label="Clear" icon={<span>X</span>} disabledReason="Permission denied" />
+);
+assert(reasonedMarkup.includes("disabled=\"\""), "a disabled reason disables the icon button");
+assert(reasonedMarkup.includes("disabled-action-tooltip"), "a disabled reason remains discoverable");
+assert(!reasonedMarkup.includes("disabledReason"), "central-only props are not passed to the DOM");
+
+const legacyMarkup = renderToStaticMarkup(
+  <AdminIconButton label="Add" icon={<span>+</span>} disabled />
+);
+assert(legacyMarkup.includes("icon-button admin-icon-button"), "the legacy wrapper delegates to the neutral component and preserves its class hook");
+assert(legacyMarkup.includes("disabled=\"\""), "the legacy disabled contract is preserved");