ci(mysql): auto-dispatch personal-cloud apply after firebase-cloud apply

[poly-glot]

Summary

Final piece of the cross-repo MySQL provisioning contract (PR #30). After every successful firebase-cloud terraform apply, fire `terraform-mysql-apps.yaml` on poly-glot/personal-cloud so any new entries in `mysql-app-catalog` get DBs + secret versions provisioned with zero manual intervention.

Trigger is unconditional (no version-change detection) — personal-cloud's apply is idempotent so re-runs that find no work are cheap, and false-negatives in change-detection would leave new apps unprovisioned.

Uses `MYSQL_APPS_DISPATCH_TOKEN` (fine-grained PAT, scope: `actions:write` on poly-glot/personal-cloud only).

Test plan

• CI plan: terraform.tfstate has no diffs (this is a workflow change, not a terraform change). Apply also no-ops on terraform.
• After this PR merges, the apply job runs but does NOT trigger personal-cloud (because the workflow file change isn't picked up until next terraform/** push triggers it). True smoke test happens on the next firebase-cloud terraform PR.
• Optional: trigger a no-op terraform apply (re-run the latest firebase-cloud workflow run from the GitHub UI) to verify the new dispatch step runs successfully.