experiment: add independent Core Profile implementation challenge

[bglassy]

Adds a small public interoperability challenge for the experimental SPP Core Profile.

The challenge asks third parties to implement the profile independently from the specification and canonical fixtures, without consulting the existing native or OPA reference implementations during the first pass.

Includes:

• concise challenge README
• report template
• 8 normalized expected outputs
• comparison-only self-check script
• references to the canonical Core Profile fixtures

Validation:

• expected outputs verified against canonical fixture expectations: 8/8
• self-check comparison: 8/8 matched

This challenge is experimental and non-normative.

It does not:

• modify SPP 0.1
• modify evaluator semantics
• introduce new policy semantics
• add admission/trust/lifecycle/planner behavior
• claim certification or standards endorsement