Clarify MEAD Audius user ID format

[raymondjacobson]

Summary

• Clarify that MEAD AudiusUserId values should be Audius API/SDK hash IDs, not numeric database IDs or handles.
• Replace the placeholder standalone MEAD example value with a valid hash-ID-shaped example.

Follow-up to #14509. Related implementation: AudiusProject/ddex-processor#28

Test plan

• git diff --check
• env PATH=/Users/ray/.cache/codex-runtimes/codex-primary-runtime/dependencies/node/bin:$PATH npm --workspace docs-audius-org run build

The docs build completed successfully; it still prints the existing React hideExternalIcon DOM-prop warning during prerendering.

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Latest commit: 13cd9cd

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