Add optional radio instance registry validation

[emuehlstein]

Summary

Adds an optional instance-registry contract for profile validation and resolved output provenance.

Changes

• Add instance registry schema:
  • schemas/instance-registry-0.1.schema.json
• Add optional loader/validator in profile pipeline:
  • src/codeplugger/profile.py
• Add optional CLI flag:
  • --instance-registry path/to/instances.yml
• Enforce join checks when registry is provided:
  • profile radio_instance (or profile id fallback) must exist in registry
  • registry entry radio must match profile radio
• Thread optional instance metadata into resolved model:
  • ResolvedCodeplug.radio_instance
  • src/codeplugger/resolved.py
• Add tests for missing instance, radio mismatch, and metadata propagation:
  • tests/test_profile.py
• Keep CHIRP test compatibility with resolved model update:
  • tests/test_chirp_csv.py
• Add README docs for instance registry usage:
  • README.md

Validation

• pytest -q
• Result: 21 passed

Notes

• Instance registry is optional; existing profile workflows remain backward compatible when --instance-registry is not supplied.