Add product validation control plane

[hudsonaikins]

Problem

Command-level tests do not prove product outcomes, AI semantics, visual correctness, or operational cost boundaries.

Outcome

Adds exact-head product validation contracts with typed evidence for schema, semantic, workflow, visual, operational, and security checks. Decisions fail closed as passed, failed, or blocked. Unknown required cost telemetry blocks readiness.

Adds tabellio-validate gate for CI enforcement and preserves v0.1 manifest/result compatibility.

Validation

• npm run check: 91 tests passed
• npm pack --dry-run --json: passed for 0.4.0
• focused validation CLI gate test: passed
• validation runner line coverage: 95.38%
• Fallow: zero dead-code/dependency findings; advisory complexity score assumes zero coverage and reports duplicated validation/test helpers

Rollout

Draft until consumer-repository manifests are exercised against this exact commit. Merge and release remain separately approval-gated.