Apply brand identity to the frontend (ink + bronze + paper)

Replaces the default black/gray with the docs/brand palette: warm ink text on paper surfaces, bronze accent, serif headings and the Origin-mark wordmark in the header, favicon, and the 'where it came from matters' tagline. Light/dark adapt via CSS vars (ink/paper flip); bronze and paper are constant. Tailwind v4 @theme exposes bronze/paper/ink tokens and the serif stack. Buttons/inputs/cards restyled to match; brand SVGs vendored into public/.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Signed-off-by: Justin Paul <justin@jpaul.me>

frontend/components/ui/input.tsx

@@ -7,7 +7,7 @@ export const Input = React.forwardRef<HTMLInputElement, React.InputHTMLAttribute
     <input
       ref={ref}
       className={cn(
-        "flex h-10 w-full rounded-md border border-neutral-300 bg-transparent px-3 py-2 text-sm placeholder:text-neutral-400 focus-visible:outline-none focus-visible:ring-2 focus-visible:ring-neutral-400 disabled:opacity-50",
+        "flex h-10 w-full rounded-md border border-[var(--border)] bg-[var(--surface)] px-3 py-2 text-sm placeholder:text-[var(--muted)] focus-visible:outline-none focus-visible:ring-2 focus-visible:ring-bronze disabled:opacity-50",
         className,
       )}
       {...props}