Add note on indexer ledger data defaults

[kaankacar]

Adds a one-line note to the Indexers overview about providers exposing the latest ledger data.

[github-actions]

🤖 Claude docs review

Verdict: NEEDS-CHANGES

Reviewed head 37291ff (docs/data/indexers/README.mdx, +2/−0).

Mechanics pass

• ✓ No links, images, or code fences added; MDX still compiles (plain paragraph, no unclosed tags).
• ✓ No secrets or personal data.
• ✗ (nit, non-blocking) docs/data/indexers/README.mdx:115 — the new paragraph is appended after the reference-style link-definition block (lines 103–113). It renders, but body prose belongs above the link definitions; also consider a Docusaurus :::note admonition instead of a literal "Note:" prefix.

Technical accuracy pass

• ✗ BLOCKING — docs/data/indexers/README.mdx:115 claims "as of Stellar's Protocol 28 upgrade (now live on Mainnet)". There is no Protocol 28. The current Mainnet protocol is 27 ("Zipper", activated 2026-07-08, CAP-0071); before that, 26 ("Yardstick") went live 2026-05-06 (confirmed via SDF blog "Yardstick, Stellar Protocol 26", stellar.org, dated 2026-05-05; checked via Raven corpus 2026-07-17 — no dated source for any Protocol 28 announcement or activation exists). The current first-party Stellar dev skills are likewise written against protocol 27 as the newest release. Per the priority rubric this is P1-class content: a wrong protocol/version status.
• ✗ The substantive claim — that a protocol upgrade caused "indexer providers [to] expose the latest ledger data by default" — is unsupported. Indexer freshness is a per-provider ingestion property (several listed providers are not even launched yet, e.g. Alchemy/Allium per docs/data/indexers/README.mdx:30-32; OBSRVR Flow is in private beta, line 67), not something a protocol upgrade sets "by default". I could find no source for this claim.

Completeness pass

• ✓ The diff does what the description says (adds a one-line note) — but what it adds is factually wrong, so the addition does not stand on its own.
• No related open PRs or sequencing constraints found.

What needs human/author judgment: the sentence should be removed or rewritten around a verifiable claim. I am not proposing a self-fix because there is no obviously correct replacement text — simply swapping "28" for "27" would still leave the unsupported "latest ledger data by default" assertion, and Protocol 27 (authentication delegation) has no bearing on indexer data freshness.