feat(frontend): add archive format family, compression control, and fixed double-extension parsing

Also adds a --color-family-archives CSS variable (light + dark) that
the plan didn't call out explicitly but is needed for the new family
tile/icon to render with a color instead of falling back silently.

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

frontend/src/components/FormatsGrid.jsx

@@ -1,5 +1,5 @@
 import { useTranslation } from 'react-i18next';
-import { Image, FileText, TextAa, BookOpen } from '@phosphor-icons/react';
+import { Image, FileText, TextAa, BookOpen, Archive } from '@phosphor-icons/react';
 import { FORMAT_FAMILIES } from '../data/formats.js';
 
 const FAMILY_ICONS = {
@@ -7,6 +7,7 @@ const FAMILY_ICONS = {
   documents: FileText,
   fonts: TextAa,
   ebooks: BookOpen,
+  archives: Archive,
 };
 
 export function FormatsGrid() {