Update skills for new PlanetScale CLI operations

[cursor]

Summary

Updates the PlanetScale skills for new CLI-accessible operations announced in the changelog:

• https://planetscale.com/changelog/cli-postgres-pgbouncer — documents read-only PgBouncer inventory via pscale pgbouncer list/show and gates create/resize/delete/retarget operations.
• https://planetscale.com/changelog/cli-postgres-ip-restrictions — adds CLI inventory guidance for database-level Postgres IP restrictions and classifies create/update/delete as network access changes.
• https://planetscale.com/changelog/cli-backup-policy — adds scheduled backup policy inventory guidance for Postgres and Vitess and treats policy mutations as recovery-posture changes.
• https://planetscale.com/changelog/cli-database-update — classifies database setting updates such as default branch and region restrictions as approval-gated changes.
• https://planetscale.com/changelog/auth-attempt-exports-cli — adds handling guidance for Postgres authentication-attempt exports because they include client IPs, credential identifiers, usernames, outcomes, and failure details.

Validation

• git diff --check HEAD~1..HEAD