Automated ES/EN README parity gate for version, commands, and essential links

[klssxx]

Context

THEKEY ships normative docs in Spanish (README.md, THREAT_MODEL.md, CONTRIBUTING.md) and English (README.en.md, THREAT_MODEL.en.md, CONTRIBUTING.en.md). A divergence in version, commands, or essential links would be a publication blocker.

Requisito o riesgo al que responde

• Requisito: THEKEY_CONTRACT §5 (Every run is auditable) — the docs a visitor reads must match the engine's actual behavior.
• Riesgo cubierto: THREAT-T3 (weak/divergent policy) applied to documentation — a drifted README misleads contributors about commands and guarantees.

Impacto si no se resuelve

A contributor following the EN README could run a stale command or assume a guarantee the ES version dropped; the parity promise of the project breaks and triage starts with a doc bug.

Acceptance criteria

• scripts/ci/parity_gate.py asserts: project version 0.2.0, Quick Start commands (git clone / cd THEKEY / demo.ps1), main demo command (python -m thekey demo), presence of "workflow isolation" claim and absence of any OS-sandbox claim, presence of "deterministic policy authorization" (not "auto-approval"), and essential doc cross-links.
• A seeded divergence (temporarily drop the demo command from README.en.md) makes the gate exit non-zero (negative test proven in CI).
• CI job docs-gates runs the gate on every PR.
• CONTRIBUTING documents the parity requirement.

Cómo se verifica

python scripts/ci/parity_gate.py
# expected: exit 0, prints PASS for every invariant
python -m thekey demo
# expected: RELEASE_ELIGIBLE, gates_passed: 4/4

Evidencia en event store

This is a CI/docs gate, not a transactional change. On merge, the PR must record: Closes #1, green pytest -q + parity_gate.py output pasted in the PR body, and python -m thekey demo reaching RELEASE_ELIGIBLE with evidence_mismatches: [] (hash chain intact).

Docs afectados

• README / README.en actualizado (if any command changed)
• CHANGELOG entrada añadida
• DECISIONS.md si hay decisión de diseño