Standardize real-screen evidence manifests without rewriting history

[aruintelligence]

Adds a forward-looking, machine-readable contract for ĀML real-screen experiment evidence.

Changes:

• adds schema/real-screen-evidence-manifest.schema.json;
• documents the canonical corpus shape in evidence/real-screen/README.md;
• requires source/capture provenance, artifact hashes, label provenance, exact ĀML version/policy, receipt binding, rerun status, explicit evidence eligibility, and claim boundaries for new manifests;
• explicitly treats pre-contract experiment directories as legacy/unmigrated unless existing artifacts can be mapped without inventing missing evidence;
• adds tests for the evidence-boundary rules.

This does not rewrite historical captures or manufacture missing timestamps, screenshots, hashes, browser metadata, or production after-states. Project-authored reviewer labels remain declared judgments, not objective cognitive measurements or independent validation.