Add Prophet Intelligence Foundry contract spine

[mdheller]

Summary

• Adds schemas/prophet-foundry-contract-spine.schema.json as a v0.1 contract spine for Prophet Intelligence Foundry work.
• Adds examples/prophet-foundry-contract-spine.example.json as a machine-checkable fixture.
• Adds docs/prophet-intelligence-foundry-v0.1.md defining the Foundry boundary, required contract families, promotion law, and runtime law.
• Updates Makefile so make validate checks the new schema and fixture.
• Updates README to advertise the Foundry spine without implying runtime readiness.

Validation

• Authored the schema and example as JSON and validated them locally with Python/jsonschema before pushing.
• Compared branch against main: 5 commits ahead, 0 behind.
• Changed files are limited to README, Makefile, docs, schema, and example fixture.

Boundary notes

This PR intentionally does not add runtime code, model weights, mutable adapters, training data, or SourceOS image state. It reserves contract-family names and authority boundaries so downstream runtime work does not invent competing semantics.