Import dropdown: pull a zone live from a public resolver

[fsjobeck]

Summary

The "Import…" button is now a dropdown:

• From file… — current file picker
• From public DNS — one entry per configured DoH resolver (Cloudflare, Google, DNS.SB)

Picking a resolver opens a small inline form for a domain. On submit we fan out DoH queries to that single resolver for:

• Apex RR types: SOA, NS, A, AAAA, MX, TXT, CAA
• Well-known subdomain probes: www, _dmarc, mail, autodiscover

…and assemble a `Zone` from the answers. SOA TTL becomes the zone-level `$TTL`; per-record TTLs come straight from the resolver.

Why

• Faster than copy-pasting from a registrar UI
• Matches the existing propagation-check infrastructure (same resolvers, same allowlist)
• Honest: per-type errors are surfaced through the existing parseErrors panel, so partial imports stay usable

What's new

File	What
`src/dns/import.ts`	Pure fan-out logic; converts DoH answers to ZoneRecords
`src/components/ImportMenu.tsx`	Replaces the bare Import button — dropdown + inline domain form
`src/hooks/useZoneFile.ts`	New `importFromDns()` + `isResolving`
`src/components/Topbar.tsx`	Wires the new menu in; old refs/file-input markup removed
`src/styles.css`	Dropdown + inline-form styles
`tests/dns-import.test.ts`	9 new tests (apex fan-out, MX/TXT/SOA shape, domain normalization, error paths)

Test plan

• CI passes (build + audit + 116 vitest)
• In dev: click Import → menu shows; pick Cloudflare → enter `codabind.com` → records populate
• Bad domain (e.g. `asdf`) yields a parseErrors entry, not a crash
• Esc / outside-click closes the dropdown
• Import button shows "Resolving…" while in flight

Notes

• We can't enumerate all subdomains via public DoH (that would require AXFR), so subdomain probes are a curated list. Users can edit / add records normally after the import.
• No CSP changes — the resolver hosts are already in `connect-src`.

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