[Fundamentals] Update Organization account and zone limits

[ally-cf]

Summary

Updates the Organizations documentation to reflect default limits of 20,000 accounts and 200,000 zones across a root Organization hierarchy. It also documents per-Organization configuration, preserves the legacy Tenant distinction, and adds a changelog entry.

This PR should not merge until the new account and zone limits are enabled and validated in production.

Documentation checklist

• Is there a changelog entry (guidelines)? If you don't add one for something awesome and new (however small) - how will our customers find out? Changelogs are automatically posted to RSS feeds, the Discord, and X.
• The change adheres to the documentation style guide.
• An issue tracks the outdated information corrected by this PR.

[nickzylstra]

approved assuming my comment is addressed

[cloudflare-docs-bot]

AI Review

✅ Reviewed 941fa80 · 0 findings · incremental

Resolved (1) · Dismissed (0)

• Resolved: Remove please from prose · Verified at head via read_repo_file: line 12 now reads "If you require a higher limit, reach out to your account team." — please has been removed from the prose, satisfying the core-content style rule.

Commands

• /review Run a review now.
• /full-review Review the entire PR diff.
• /disable-auto-review Stop automatic reviews.
• /rebase Rebase against production.

[cloudflare-docs-bot]

Review coverage

🟡 2 ownership areas need approval.

Suggested reviewers: @AdamBouhmad

Needs approval	Eligible approvers	Suggested
fundamentals /src/content/docs/fundamentals/	@adambouhmad, @jhutchings1, @sahidya, @cloudflare/product-owners	adambouhmad
fundamentals /src/content/changelog/fundamentals/	@adambouhmad, @jhutchings1, @sahidya, @cloudflare/pm-changelogs, @cloudflare/product-owners	No suggestions

CODEOWNERS mappings for displayed areas (2)

Pattern	Owners
/src/content/docs/fundamentals/	@adambouhmad, @jhutchings1, @sahidya, @cloudflare/product-owners
/src/content/changelog/fundamentals/	@adambouhmad, @jhutchings1, @sahidya, @cloudflare/pm-changelogs, @cloudflare/product-owners

[cloudflare-docs-bot]

⚠️ @ally-cf This pull request adds a changelog entry dated in the past:

• src/content/changelog/fundamentals/2026-10-02-organization-account-zone-limits.mdx — dated 2026-10-02

Typically, changelog entries should be dated the day they merge. This is not blocking — if the date is unintentional, please update it.