test: make test_health portable for scratch clones (#245)

Use sys.executable with optional GITEA_TOOLS_TEST_PYTHON override instead of
hard-coded venv/bin/python. Add subprocess timeouts/teardown and skip when no
interpreter is available. Note scratch-clone norm in review-pr template.

Co-Authored-By: Claude Opus 4.8 (1M context) <[email protected]>

skills/llm-project-workflow/templates/review-pr.md

@@ -36,6 +36,8 @@ Rules (llm-project-workflow):
   report the starting worktree path and whether it was dirty. If unrelated
   tracked files exist outside the PR scope, STOP or run
   `scripts/worktree-review <pr-head-branch>` and validate in the scratch path.
+  Scratch-clone validation is the norm; tests must not assume the shared
+  development worktree or a repo-local ``venv/`` (#245).
   NEVER run `git stash`, `git stash pop/drop`, `git checkout --`, `git reset`,
   or `git clean` to manage another session's dirty files.
 - Final report must state: Worktree path, Worktree dirty (yes/no),