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/button.tsx

@@ -4,13 +4,15 @@ import { cva, type VariantProps } from "class-variance-authority";
 import { cn } from "@/lib/utils";
 
 const buttonVariants = cva(
-  "inline-flex items-center justify-center rounded-md text-sm font-medium transition-colors focus-visible:outline-none focus-visible:ring-2 focus-visible:ring-neutral-400 disabled:pointer-events-none disabled:opacity-50",
+  "inline-flex items-center justify-center rounded-md text-sm font-medium transition-colors focus-visible:outline-none focus-visible:ring-2 focus-visible:ring-bronze focus-visible:ring-offset-1 disabled:pointer-events-none disabled:opacity-50",
   {
     variants: {
       variant: {
-        default: "bg-neutral-900 text-white hover:bg-neutral-700",
-        outline: "border border-neutral-300 bg-transparent hover:bg-neutral-100",
-        ghost: "hover:bg-neutral-100",
+        // Bronze is the brand accent; paper reads cleanly on it.
+        default: "bg-bronze text-paper hover:bg-bronze-deep",
+        outline:
+          "border border-bronze text-bronze bg-transparent hover:bg-bronze hover:text-paper",
+        ghost: "text-[var(--foreground)] hover:bg-bronze/10",
       },
       size: {
         default: "h-10 px-4 py-2",