fix(web): start CTAs → /auth/register + GitHub link → claude-intercom OSS

All conversion CTAs were pointing to the dead github.com/claudemesh/
claudemesh repo or # hash fragments. Landing is the primary funnel for
v0.1.0 — every "Start" button is a conversion-critical surface.

Fixes:
- Header "Start free" → /auth/register
- Header GitHub nav item → REMOVED (kept the icon button, repointed)
- Hero "Start free" → /auth/register
- Pricing 6× CTAs: Solo/Pro/Plus/Team/Business → /auth/register,
  Enterprise → /contact
- CTA footer "Star on GitHub" → /auth/register ("Start free")
- BeyondTerminal "Read the protocol spec" → /auth/register
  ("Get on the mesh")

GitHub reinstated as a dedicated icon button in the header right side,
pointing to https://github.com/alezmad/claude-intercom — the MIT OSS
foundation claudemesh is built on. Honest provenance: claude-intercom
is the local peer-mesh gift to the community, claudemesh is the hosted
cross-machine extension.

Tooltip: "Built on claude-intercom · MIT open source".

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

apps/web/src/modules/marketing/home/cta.tsx

@@ -39,12 +39,11 @@ export const CallToAction = () => {
         <Reveal delay={3}>
           <div className="mt-12 flex flex-col items-stretch justify-center gap-3 sm:flex-row sm:items-center">
             <Link
-              href="https://github.com/claudemesh/claudemesh"
-              target="_blank"
+              href="/auth/register"
               className="group inline-flex items-center justify-center gap-2 rounded-[var(--cm-radius-xs)] bg-[var(--cm-clay)] px-6 py-3.5 text-[15px] font-medium text-[var(--cm-fg)] transition-colors duration-300 hover:bg-[var(--cm-clay-hover)]"
               style={{ fontFamily: "var(--cm-font-sans)" }}
             >
-              Star on GitHub
+              Start free
               <span className="transition-transform duration-300 group-hover:translate-x-0.5">
                 →
               </span>