feat: initialize governed postbox module

webui/scripts/test-postbox-page-structure.mjs

@@ -0,0 +1,29 @@
+import assert from "node:assert/strict";
+import { readFileSync } from "node:fs";
+
+const page = readFileSync(
+  new URL("../src/features/postbox/PostboxPage.tsx", import.meta.url),
+  "utf8"
+);
+const admin = readFileSync(
+  new URL("../src/features/postbox/PostboxAdminPanel.tsx", import.meta.url),
+  "utf8"
+);
+const styles = readFileSync(
+  new URL("../src/styles/postbox.css", import.meta.url),
+  "utf8"
+);
+
+assert.match(page, /postbox-shell/);
+assert.match(page, /postbox-directory/);
+assert.match(page, /postbox-message-list/);
+assert.match(page, /postbox-detail/);
+assert.match(page, /postbox\.inbox\.directory/);
+assert.match(page, /postbox\.inbox\.messages/);
+assert.match(admin, /AdminPageLayout/);
+assert.match(admin, /Postbox templates/);
+assert.match(admin, /Exact postbox/);
+assert.match(styles, /\.postbox-shell\s*\{/);
+assert.match(styles, /grid-template-columns:/);
+
+console.log("Postbox WebUI structure checks passed.");