Fix pre-existing issues and update README for v2.0

- Fix _infer_state_from_artifacts: SPEC-only maps to research (was bug_find)
- Fix cmd_validate_folder: corrupted .state files now error instead of silent fallback
- Fix upgrade.sh: remove || true, add python3 check, use git rev-parse --git-dir
- Update README.md with --project flag, --can-edit modes, --upgrade, enforcement layers
- Add 6 new tests for inference and validation fixes
- Complete hook-install-process and readme-upgrade-docs tasks

tasks/readme-upgrade-docs/DOC_REVIEW.md

@@ -0,0 +1,16 @@
+# Doc Review: README and Upgrade Docs
+
+## Review Summary
+
+All documentation changes are accurate and consistent with the v2.0 enforcement implementation.
+
+## Checklist
+- [x] `--project` flag present on all status.py command examples
+- [x] `--can-edit` 4 modes documented with examples
+- [x] `--upgrade` documented for untracked tasks
+- [x] Three enforcement layers documented
+- [x] Upgrade process is step-by-step with commands
+- [x] Pre-commit hook installation in both Project Setup and Upgrading sections
+- [x] Key Components updated with all new files
+- [x] Untracked tasks section explains the refusal behavior
+- [x] No broken markdown or formatting issues