Tighten ready-mode release record integrity

[simaba]

Problem

Ready mode rejected placeholders only in a few metadata and gate fields. Placeholder conditions, evidence paths, findings, follow-through fields, malformed evidence dates, and free-form version strings could still pass as a ready decision record.

Changes

• recursively rejects placeholders anywhere in a ready-mode payload
• validates non-empty text entries in decision lists and evidence references
• requires a decision rationale in ready mode
• validates evidence_cutoff as an ISO date
• validates version as a stable identifier token without imposing semantic versioning
• validates optional gate limitations when supplied
• expands tests for nested placeholders, evidence references, malformed dates, unstable versions, and template-mode behavior
• updates validation documentation

Limits

The validator still checks only input integrity and selected decision coherence. It does not authenticate evidence, justify gates, determine legal applicability, or approve a release.