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/index.css

@@ -23,6 +23,7 @@
   --color-family-documents: var(--color-aurora-cyan);
   --color-family-fonts: #f5a524;
   --color-family-ebooks: #10b981;
+  --color-family-archives: #64748b;
 
   --font-sans: 'Plus Jakarta Sans', system-ui, 'Segoe UI', Roboto, sans-serif;
   --font-display: 'Bricolage Grotesque', var(--font-sans);
@@ -51,6 +52,7 @@
   --color-family-documents: var(--color-aurora-cyan);
   --color-family-fonts: #ffb84d;
   --color-family-ebooks: #34d399;
+  --color-family-archives: #94a3b8;
 }
 
 *, *::before, *::after {