fix(scripts): refuse destructive --out targets and skip fork PR labelling

[TMHSDigital]

Closes #352. Closes #351.

#352: build_plugin_dist.py --out deleted any existing directory

• New unsafe_out() check, applied before anything is touched. It refuses:

  • the repo or any of its parents;
  • any directory containing .git, even with --force;
  • a non-file target;
  • a non-empty directory unless --force is given.

  A refusal exits 2.

• release.yml builds into a fresh $RUNNER_TEMP/plugin-dist, so it is unaffected. --check is unaffected too.

• New tests/test_build_plugin_dist.py (6 tests), wired into Validate. The repo-root and parent cases call unsafe_out() directly, never main(), so a future guard regression can't delete the checkout running the test.

#351: Auto-label failed on every fork PR, which would block releases

• The job runs only when head.repo.full_name == github.repository. A fork's GITHUB_TOKEN is read-only, so gh pr edit would 403, and release-gate.sh refuses a merge whose PR has a failed check.
• The unused actions/checkout is dropped. GH_REPO is set so gh works without a checkout.
• gh label create no longer passes --force, which reset existing labels' colour and description to grey on every run.

Evidence

Proven locally (Python 3.13, Windows):

• python tests/test_build_plugin_dist.py -v: 6/6 OK.
• python scripts/build_plugin_dist.py --check: plugin dist: 67 files, 0.27 MB ok.
• Falsified: in a scratch copy of the script with the guard call replaced by reason = None, three tests fail (test_refuses_non_empty_dir_without_force, test_refuses_git_checkout_even_with_force, test_force_replaces_previous_build).
• Both workflow files parse as YAML.

By inspection only: the fork if: cannot be exercised without a fork PR. This PR's own label run (same-repo) should still apply labels, which is the observable check.

🤖 Generated with Claude Code

[TMHSDigital]

CI evidence before merge: all checks pass ( 13 pass ). Blender Smoke on PR head: Blender 5.2.2 LTS / Blender 4.5.14 LTS. Summaries (happy path; falsifiers) per leg: 143 passed, 1 skipped, 0 failed;142 passed, 0 skipped, 0 failed;141 passed, 3 skipped, 0 failed;136 passed, 6 skipped, 0 failed;