Style anchors with underline + leaf color for visibility

Body-copy mailto links ("Chris @ FCI") and the chrome nav link
were rendering as plain text, hard to spot. Added an @layer base
rule that gives every `a[href]` a 1px underline at 2px offset and
the FCI Seed Grant green, with a subtle hover thicken. Tailwind
utilities still win on a per-element basis (the nav link keeps its
`text-ink-soft` color, the brand-image wrapper opts out via
`no-underline`).

components/SiteChrome.tsx

@@ -7,7 +7,7 @@ export function SiteHeader() {
       <div className="mx-auto flex max-w-3xl items-center justify-between px-4 py-5 sm:px-6">
         <Link
           href="https://fci.coop"
-          className="group flex items-center gap-4 focus:outline-none"
+          className="group flex items-center gap-4 text-ink no-underline focus:outline-none"
           aria-label="Food Co-op Initiative — fci.coop"
         >
           <Image