Migrate avy-fx.org domain, email & infra to Avy (rebrand Tier 2)

[busbyk]

This was generated by AI during triage.

Tier 2 of the AvyFx → Avy rebrand (#647): migrating the functional avy-fx footprint — domains, email addresses, and external services. Split out from #647 because, unlike the display rename, this requires external-service access and a domain decision, so it can't be delegated to an AFK agent.

Depends on #647 for the display/branding side; this issue is the infra half of the same rebrand.

Brief (ready-for-human)

Category: enhancement
Summary: Migrate the avy-fx domain, email addresses, and external-service references to the new "Avy" brand.

Why this needs a human (not an AFK agent):

• A domain must be chosen and acquired first — there is no confirmed "Avy" domain in the code today. This is a branding/procurement decision, not a code change.
• Requires access to external systems: the DNS registrar, Vercel domain config, the email provider (Resend — SPF/DKIM/deliverability), and Notion.
• It's a production cutover that must be sequenced to avoid breaking live sites and email delivery.

Scope (the functional avy-fx footprint):

• Production domain avy-fx.org → the new Avy domain: DNS, Vercel domains, redirects from the old domain, and NEXT_PUBLIC_ROOT_DOMAIN.
• Email addresses support@avy-fx.org and noreply@avy-fx.org (the default from-address / adapter and the contact-form sender) → new-domain addresses, with email-provider config and deliverability verification.
• Help links avy-fx.notion.site (in the logout button and the getting-started dashboard widget) → the new Notion/help URL.
• Template-tenant demo domain avy-fx-demo.org (the DVAC template tenant in the avalanche-centers definition, and referenced in docs/onboarding.md).

Acceptance criteria:

• A new Avy domain is chosen, acquired, and serving the platform; avy-fx.org redirects to it (no broken links).
• Platform email sends from the new-domain addresses with SPF/DKIM verified; contact-form and transactional emails deliver.
• Help links point to the current Notion/help location.
• The template-tenant demo domain and docs/onboarding.md reference the new domain.
• No lingering references to avy-fx.org / avy-fx-demo.org / avy-fx.notion.site in code or docs.

Out of scope:

• Display/branding strings and logo — that's AvyFx branding -> Avy #647 (Tier 1).
• New brand artwork (icon / OG image).

Open decision for the maintainer: what is the new domain? Everything here waits on that.

[busbyk]

This was generated by AI during triage.

Tier 1 (display/branding rename) is specified and ready in #647. This issue is the infra half and depends on it.