Toolchain Readiness in doctor and contract

[BramVR]

Parent

#70

What to build

Add the first Toolchain Readiness tracer with declaration and result shapes plus fake detection. doctor and Agent Run Contract should be able to include toolchain status without CodeMesh installing or building environments.

Acceptance criteria

• Project Policy can declare toolchain readiness requirements without invoking installers.
• Fake detection adapter reports present, missing, and unknown toolchain statuses.
• doctor includes toolchain readiness in human and JSON output.
• Agent Run Contract includes toolchain status when checked.
• Tests prove CodeMesh reports/delegates only and does not build environments.

Blocked by

• Agent Run Contract v1 baseline #73
• codemesh doctor preflight with strict mode #75