docs: note 1MB payload limit for custom attestations

[sami-alajrami]

Documents the 1MB size limit on the --attestation-data payload for kosli attest custom.

Ref: kosli-dev/server#5388

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[claude]

Claude finished @sami-alajrami's task in 52s —— View job

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Doc review

• Read the PR diff (git diff origin/main...HEAD)
• Read both changed files in context + CLAUDE.md conventions
• Check links, navigation, style rules
• Post review

No blocking findings. Both earlier suggestions were applied and the two pages now agree.

Verified

• 1 MB (with space) on both pages — matches the only other size unit in the repo (changelog/index.mdx:1056, "~400-500 KB").
• Both pages say JSON payload, so readers won't measure a pretty-printed file against the wire size.
• The 400 error is stated in both places, so the symptom that brings people here is searchable.
• /tutorials/attest_large_documents is root-relative, the file exists, and it's already in config/navigation.json:93. No new pages, so no navigation changes needed.
• mint broken-links isn't runnable here (CLI not installed on the runner) — I verified the one added link by hand instead.

Suggestion (optional, non-blocking) — getting_started/attestations.md:206
The --user-data and --attachments blocks above each follow a prose → code block rhythm; the new paragraph lands between the --attestation-data prose and its example, breaking that pattern. Moving it below the code block at line 217 would keep the rhythm. Reasonable to leave as-is if you want the limit visible before the example.

The open question about whether the same cap applies to --user-data (documented directly above on the same page) is worth a follow-up once you can confirm it server-side — readers on this page will naturally wonder. Not something to hold this PR for.
· branch docs/attest-payload-size-limit