Update skills for Vitess request size Insights

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Summary

• Update Query Insights guidance for the new Vitess bytes-received/request-size metrics.
• Add the same signal to read-only inventory, Vitess safety review, and best-practices matrix checklists so assessments inspect large inbound query payloads alongside existing Insights metrics.

Changelog entry

• https://planetscale.com/changelog/insights-bytes-received-mysql

Why

PlanetScale Query Insights for Vitess now tracks bytes received, bytes received per query, and max bytes received per query. These metrics help agents identify clients sending unusually large statements or parameter payloads, and they pair with existing bytes returned metrics to explain query network traffic in both directions.

Validation

• Confirmed the feed entry was newer than the stored automation high-water mark.
• Verified the new guidance appears only in the affected SKILL.md files.
• Markdown-only change; no automated test suite was present or required.