feat(frontend): redesign homepage and file config form with aurora palette

Rebuild the visual identity from the actual Ombrora mark (violet/cyan aurora
blobs) instead of the generic blue/amber scheme, add Bricolage Grotesque and
IBM Plex Mono for display and code-like text, and give the hero an animated
aurora backdrop, gradient headline, and a format-pair marquee driven by the
real registered converters.

Rework the file config form: target format and icon size are both chip
groups now instead of a native select, and quality/compression sliders get a
gradient-filled track, custom thumb, and a mono value pill to match. File
type icons are color-coded by family (images/documents/fonts/ebooks) and
reused across FileConfigCard, FileCard, and FormatsGrid.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

frontend/src/api.js

@@ -4,6 +4,11 @@ export async function fetchFormats(source) {
   return data.targets;
 }
 
+export async function fetchConfig() {
+  const response = await fetch('/api/config');
+  return response.json();
+}
+
 export async function uploadFiles(items) {
   const formData = new FormData();
   const targetFormats = [];