Update PlanetScale skills for Postgres switchovers

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Summary

• Update Postgres inventory, safety review, best-practices matrix, and report guidance for on-demand Postgres switchovers.
• Classify branch switchovers/restarts in the approval and MCP operating-model docs as non-default operational mutations.
• Document pscale branch switchover CLI behavior, candidate selection, single-instance restart behavior, and the pscale 0.322.0+ requirement.

Changelog source

• https://planetscale.com/changelog/postgres-switchovers

Why

The changelog introduces on-demand Postgres primary switchovers via dashboard, CLI, and API. This affects the skills because agents should collect switchover-readiness evidence, treat production switchovers as availability-impacting operations, and avoid triggering them without explicit approval.

Verification

• git diff --check origin/main...HEAD
• git status --short --branch