fix(ui): use absolute paths for modal assets

Updates `profile-modal.html` and `application-form.html` to use root-relative paths for images and iframes, fixing 404 errors in E2E tests. Adds a preflight check to `tests/e2e/ui-modals.spec.ts` to verify asset availability.

components/application-form.html

@@ -46,7 +46,7 @@
     <div id="nostrFormModalDescription" class="modal-body">
       <div class="modal-embed-frame">
         <iframe
-          src="./components/iframe_forms/iframe-application-form.html"
+          src="/components/iframe_forms/iframe-application-form.html"
           class="h-full w-full rounded-lg border border-border/30 shadow-sm"
           frameborder="0"
         ></iframe>