fix(dash0): accept multiple DNS expected IPs/values via chip input

[fclairamb]

Summary

• The DNS check form had no way to assert on what a lookup actually resolved to — it could only confirm the lookup succeeded, even though the backend has long supported expected_ips (A/AAAA) and expected_values (CNAME/MX/NS/TXT).
• A/AAAA record types now get an "Expected IPs" chip input, validated as IPv4/IPv6 respectively — invalid entries render as a destructive chip and block save.
• Every other record type gets an "Expected values" textarea (one entry per line) — a textarea rather than chips because TXT values legitimately contain spaces (e.g. SPF records) that a chip input would split on.
• Leaving the field empty preserves today's behavior (only require a successful resolution). Switching record type always writes only the matching config key, never both — the backend rejects a config carrying both expected_ips and expected_values.

BREAKING CHANGE: none.

Test plan

• make build-dash0 clean
• bun run lint unchanged at the pre-existing 45-error baseline (only pre-existing-pattern warnings in the touched file, no new errors)
• Frontend unit tests (vitest): fromConfig/toConfig seeding and serialization (IP vs values, mutual exclusivity, empty-omission, round-trip), plus IPv4/IPv6 validator edge cases — 11/11 passing