CR-032: Model route manifest schema

[coreytshaffer]

Summary

Defines the canonical manifest artifact for model-route provenance and integrity.

• adds docs/security/model_route_manifest_schema.md
• adds concrete example manifests for local, cloud, and invalid alias-only routes
• distinguishes required and optional provenance fields
• pins down local/cloud boundary, backend identity, model identity, artifact integrity, quantization, and template metadata
• keeps CR-032 documentation-only

Validation

• python -m pytest -q
• tc identity check
• tc audit --privacy-invariants
• tc audit --verify-signatures

Notes

This PR defines the artifact contract for future runtime checks. CR-033 should validate manifests against this schema rather than inventing route-provenance rules ad hoc in code.