Wire loopover.ai as a live secondary domain

[JSONbored]

Problem: loopover.ai is purchased and DNS-live on Cloudflare but isn't wired to anything. gittensory.aethereal.dev is still the only working domain for the product.

Area: Infra / Cloudflare

Proposal: Add loopover.ai as a secondary custom domain on the existing UI Worker (and the API Worker for its subdomain), alongside the current domain. No code change should be required — the site already resolves its public URL through an overridable default rather than a hardcoded literal.

Deliverables:

• loopover.ai resolves to the live site over TLS.
• The existing domain keeps working unchanged, side-by-side.
• OAuth callback URLs cover the new domain if the auth flow is domain-sensitive.

Acceptance criteria:

• loopover.ai loads the current site with valid TLS.
• gittensory.aethereal.dev continues to work unchanged.
• GitHub OAuth sign-in completes successfully from both domains.

Test scenarios:

• Fresh browser session to loopover.ai end-to-end (load, sign in, sign out).
• Existing bookmarked links to the old domain still resolve correctly.

Resources:

• The site's default-public-URL constant and its documented override mechanism (self-hosters already override this via an environment variable).
• Worker route configuration for both the UI and API Workers.

Boundaries:

• No changes to site/, CNAME, or any legacy static-docs path (all out of scope / blocked paths).
• Don't touch anything under the separate gittensor network's own domain — that's a different, unrelated brand and is never touched by this rename.
• No redirect yet — that's Decide & schedule the domain sunset window #4765, on its own schedule.

---

Part of #4761.

[linear-code]

JSO-3434