feat(invite): branded email + one-command install+launch UX

Email (broker):
- Rebrand mesh-invitation.tsx to match site (clay accent #d97757,
  cream fg, Anthropic Serif/Mono, dark bg). Mesh glyph in header.
- Hero CTA links to the /i/short URL landing page.
- Single one-liner 'npm i -g claudemesh-cli && claudemesh launch --join URL'
  so new users copy once, paste once, done.

Web InstallToggle:
- Replace two-step numbered list with single one-liner in the first-time
  panel. Reduces copy/paste ops from 2 to 1 and stops prescribing
  'YourName' as a literal (CLI now defaults to $USER).

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

apps/broker/src/index.ts

@@ -5143,7 +5143,7 @@ async function handleCliMeshInvite(req: IncomingMessage, slug: string, res: Serv
           const { MeshInvitation } = await import("./emails/mesh-invitation");
           const React = await import("react");
           const subject = `You're invited to join "${m.name}" on claudemesh`;
-          const element = React.createElement(MeshInvitation, { meshName: m.name, inviteUrl: url, expiresAt: expiresAt.toISOString(), appBaseUrl: baseUrl });
+          const element = React.createElement(MeshInvitation, { meshName: m.name, inviteUrl: url, token, expiresAt: expiresAt.toISOString(), appBaseUrl: baseUrl });
           const html = await render(element);
           const text = await render(element, { plainText: true });
           const res = process.env.POSTMARK_API_KEY