Harden codex-project-kit installer/test/CI workflow

[nakazanie-ton]

Summary

• add LICENSE and SECURITY policy files
• harden installer argument parsing and target validation
• add reusable JSON validator and wire it into bootstrap normalization
• expand kit test gates with shellcheck/JSON checks and stronger bad-config assertions
• install shellcheck in CI before running scripts/test_kits.sh

Validation

• bash -n scripts/.sh kits/codex-bootstrap-kit/bin/install.sh kits/codex-taskflow-kit/bin/install.sh kits/codex-bootstrap-kit/templates/scripts/.sh kits/codex-taskflow-kit/templates/scripts/*.sh
• python3 -m py_compile kits/codex-bootstrap-kit/templates/.codex_bootstrap/bootstrap/generate_codex_state.py kits/codex-taskflow-kit/templates/.codex_taskflow/taskflow_engine.py
• bash scripts/test_kits.sh