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/utils/fileFamily.js

@@ -0,0 +1,22 @@
+import { Image, FileText, TextAa, BookOpen, File as FileIcon } from '@phosphor-icons/react';
+import { FORMAT_FAMILIES } from '../data/formats.js';
+
+const FAMILY_ICONS = {
+  images: Image,
+  documents: FileText,
+  fonts: TextAa,
+  ebooks: BookOpen,
+};
+
+export function familyForExtension(extension) {
+  const ext = extension?.toLowerCase();
+  return FORMAT_FAMILIES.find((family) => family.formats.includes(ext))?.key ?? null;
+}
+
+export function fileTypeMeta(extension) {
+  const family = familyForExtension(extension);
+  return {
+    Icon: FAMILY_ICONS[family] ?? FileIcon,
+    colorVar: family ? `--color-family-${family}` : '--color-primary',
+  };
+}