refactor(webui): use central mailbox icon action

webui/scripts/test-mailbox-icon-button-structure.mjs

@@ -0,0 +1,25 @@
+import fs from "node:fs";
+import path from "node:path";
+import { fileURLToPath } from "node:url";
+
+const webuiDir = path.resolve(path.dirname(fileURLToPath(import.meta.url)), "..");
+const source = fs.readFileSync(path.join(webuiDir, "src/features/mail/MailboxPage.tsx"), "utf8");
+const styles = fs.readFileSync(path.join(webuiDir, "src/styles/mail-profiles.css"), "utf8");
+
+function assert(condition, message) {
+  if (!condition) throw new Error(message);
+}
+
+assert(source.includes("IconButton,"), "MailboxPage must import the central IconButton");
+assert(
+  source.includes('<IconButton label="i18n:govoplan-mail.clear_message_search.cc9f2800"'),
+  "the clear-search action must use the central IconButton"
+);
+assert(
+  !source.includes('<button type="button" onClick={() => setMessageQuery("")}'),
+  "the raw clear-search button must not return"
+);
+assert(
+  !styles.includes(".mailbox-search-field button"),
+  "Mail must not redefine the central icon-button appearance"
+);