Add pre-commit hooks for Objective favorite and mujoco_viewer validation

[davetcoleman]

Summary

Converts the CI validation checks into local pre-commit hooks per @JWhitleyWork's feedback, so they run on every commit and as part of the existing pre-commit CI job (no additional GHA servers needed).

Adds two bash scripts under scripts/ as local pre-commit hooks:

• check_objective_favorites.sh — Enforces two rules:
  1. Non-runnable Objectives (<Metadata runnable="false"/>) must not be favorited
  2. Maximum 8 favorited Objectives per config package — if everything is favorited, nothing is favorited
• check_mujoco_viewer.sh — Ensures mujoco_viewer is not set to true in any committed config file

Both hooks are triggered by relevant file patterns (.xml and config.yaml respectively) and run via the existing format.yaml CI workflow.

Test plan

• Both scripts pass locally: bash scripts/check_objective_favorites.sh and bash scripts/check_mujoco_viewer.sh
• Both hooks pass via pre-commit run --all-files
• CI pre-commit job passes on this PR
• Verify that adding _favorite="true" to a non-runnable Objective causes pre-commit to fail
• Verify that exceeding 8 favorites in a config package causes pre-commit to fail

🤖 Generated with Claude Code

[davetcoleman]

This won't pass until #516 is merged in (and cherry picked to main), which fixes the original problem.

[JWhitleyWork]

These would be much better suited as part of the pre-commit hook. Please convert to bash scripts that can be run as part of pre-commit. This verifies their correctness on every commit and also when the pre-commit job runs as part of CI. No GHA servers required.

[davetcoleman]

Reworked per your feedback — moved from GHA workflow jobs to local pre-commit hooks (bash scripts in scripts/). They'll run on every commit and via the existing format.yaml pre-commit CI job, no additional GHA servers needed.

[JWhitleyWork]

LGTM. Thanks!