feat(loop): pin schemas v0.1.2 and verify vendor integrity

[brunovicco]

Summary

• vendor engineering-loop-schemas v0.1.2 from an exact commit
• add an offline integrity and provenance manifest
• add the loop-schema-vendor quality gate
• detect manual changes to vendored schema code
• update the pinned setup-uv action

Pinned source

• version: v0.1.2
• commit: 0459d61b7b1d4e7b46709e6d3895770553e6fab0

Validation

• 56 regression tests passed
• self-evaluation passed for all six profile/governance combinations
• compilation, Ruff, Node syntax and whitespace checks passed
• vendored bundle integrity and tampering tests passed

Scope

This remains Phase 0-1 and report-only. It does not add autonomous code modification, candidate promotion, merge or deployment.