[Registrar] Expand 7 existing docs pages with troubleshooting and FAQ content

[travisgahn]

Summary

Expands 7 existing Registrar documentation pages with troubleshooting guidance, edge case coverage, and FAQ additions. This is the second PR from the April 2026 support case gap analysis (companion to #30579 which adds 5 new pages).

Tracked in SPM-3500.

Changes

File	What was added	Est. deflection
troubleshooting.mdx	GoDaddy, Wix, Squarespace, Namecheap transfer-in sections; "registrar says unlocked but CF says locked" guidance	~15 cases/mo
renew-domains.mdx	Auto-renewal failure troubleshooting (authorization failed, 404 renewal links, failure timeline table, billing page mismatch)	~10 cases/mo
inter-account-transfer.mdx	"Cannot be moved" error checklist, inaccessible source account guidance, third-party platform domains, NS mismatch after transfer	~18 cases/mo
domain-management.mdx	Deletion troubleshooting (.uk limitation, 404 errors, token delivery, admin locks)	~12 cases/mo
transfer-domain-to-cloudflare.mdx	Auth code troubleshooting (whitespace, expiry, special chars, .ca codes, "transfer conditions not met" checklist)	~10 cases/mo
whois-redaction.mdx	Clarification that redaction is free/automatic/default, verification steps, .us exception note	~3 cases/mo
faq.mdx	6 new Q&As: failed registration refunds, double charges, domain name changes, TLD pricing, ownership letters, third-party platform registrations	~20 cases/mo

Total estimated deflection from this PR: ~88 cases/month

Context

Combined with PR #30579 (5 new pages), these two PRs address an estimated 190-220 out of ~350 monthly Registrar support cases (54-63% deflection potential).

The top gaps addressed in this PR:

• Inter-account transfer edge cases (5% of cases) — customers hit "cannot be moved" errors or have no access to the source account
• Auto-renewal failures (3%) — "authorization failed" with no troubleshooting path
• Registrar-specific transfer issues (4%) — Wix/Squarespace/GoDaddy have platform-specific behaviors not documented
• Domain deletion failures (3%) — .uk limitation, 404 errors not explained
• Auth code rejection (3%) — no troubleshooting for the most common transfer-in error

Style compliance

• Uses existing Starlight admonition syntax (:::note, :::caution)
• DashButton component used for dashboard links
• No contractions, active voice, "select" not "click"
• Internal links use relative paths without file extensions
• Tables use Markdown syntax, no HTML
• Sequential heading levels (H2 → H3 → H4)