fix(skills): require explicit date calculations

[dollarop]

Resumen

• exige mostrar el cálculo explícito antes de afirmar duraciones o vencimientos
• añade la verificación aritmética al cierre de argentina-bucles
• evita confundir fechas base, vencimientos y visualizaciones

Closes #15

Verificación

• git diff --check

[gitar-bot]

Code Review ✅ Approved

Updates the skills instructions to require explicit date calculations and arithmetic verification before stating durations or expirations, preventing confusion between base dates and views. No issues found.

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