[DNS] Clarify that assigned nameservers cannot be changed

[ngayerie]

Summary

DEE-3776

What

• DNS FAQ (dns/faq.mdx): new entry "Why does my new zone have different nameservers than my other zones?" under the existing ## Nameservers section.
• Nameserver options (dns/nameservers/nameserver-options.mdx): replace a plain sentence in Assignment method with a :::note callout that points to the new FAQ entry and to the Nameserver consistency section.
• Foundation DNS advanced nameservers (dns/foundation-dns/advanced-nameservers.mdx): new Consistent assignment across new zones subsection that explains why a new zone might get a different color set (blue / gold / orange) and cross-links Account custom nameservers.

Why

Common customer question - Support sees it regularly - "why did my new zone get different nameservers than my other zones, can you reassign it?" The docs already state that assignments cannot be changed after zone creation, but the guidance is buried in prose. This makes the answer easier to find, states the "cannot be changed" rule up front, and points customers to the two supported paths for consistent nameservers across zones (Account custom nameservers on Business/Enterprise, or DNS zone defaults on Enterprise).

Documentation checklist

• The change adheres to the documentation style guide.
• No page name or location changes; no redirects needed.
• Changelog: not applicable - clarification of existing documented behavior, no product change.

[cloudflare-docs-bot]

Review

⚠️ 1 warning, 💡 1 suggestion found in commit a2743ad.

👉 Fix in your agent 👈

Fix the following review findings in PR #33037 (https://github.com/cloudflare/cloudflare-docs/pull/33037).

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---

## Style Guide Review

### Warnings (1)

#### SG-4d9408d94024 · Headings — trailing punctuation
- **File:** `src/content/docs/dns/faq.mdx` line 95
- **Issue:** ### Why does my new zone have different nameservers than my other zones?
- **Fix:** Remove the trailing question mark from the heading.

### Suggestions (1)

#### SG-d6a51dc51dd3 · Lists — fewer than three items
- **File:** `src/content/docs/dns/faq.mdx` line 108
- **Issue:** The added options list under "To make future zones share the same nameservers..." contains only two bullet items.
- **Fix:** Convert the two-item list to prose or consolidate the items into a single sentence.

Code Review

This code review is in beta and may not always be helpful — use your judgment.

_{No code review issues found.}

Conventions

_{No convention issues found.}

Style Guide Review

Warnings (1)

File	Issue
dns/faq.mdx line 95	Headings — trailing punctuation — ### Why does my new zone have different nameservers than my other zones? Fix: Remove the trailing question mark from the heading.

Suggestions (1)

File	Issue
dns/faq.mdx line 108	Lists — fewer than three items — The added options list under "To make future zones share the same nameservers..." contains only two bullet items. Fix: Convert the two-item list to prose or consolidate the items into a single sentence.

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[hannes-cf]

Approved, once comments are addressed.