bartulem/usv-playpen: v0.10.6 — CI fix: prettier drift; harden pre-push gate

v0.10.6 — CI fix: prettier drift; harden pre-push gate

Two non-runtime changes resolving the v0.10.5 CI failure and closing the gap that let it slip past the local gate:

• _metadata.yaml reformatted by prettier (single -> double quotes on schema_version and empty-string scalars). The drift was introduced in commit 75b0ab2 but only surfaced when CI ran prettier against --all-files; local pre-commit had no reason to touch the unmodified file, so it sat in main until the v0.10.5 push finally tripped the CI Format job.

• .pre-commit-config.yaml now installs a second pre-push hook (pre-commit-format-check) that runs pre-commit run --all-files --hook-stage manual — the exact invocation the CI Format job uses. Drift in files nobody is currently editing is rejected at git push time rather than slipping past until a red CI badge. Requires a one-time pre-commit install --hook-type pre-push on each clone. The existing pre-push pytest hook is preserved; both fire on every push. Bypass with git push --no-verify.

No runtime, library, or output behavior changes vs v0.10.5.