control-plane: canonical srcos $id wrappers for legacy schemas

[mdheller]

This PR eliminates multi-authority schema identity in the control-plane tranche without breaking legacy consumers.

Problem:

• Most control-plane schemas were imported with $id under socioprophet.org, while the canonical SourceOS typed-contract namespace is schemas.srcos.ai/v2/....
• PR spec hygiene: canonicalize Truth Plane ADR + examples + schema IDs #35 normalized IncidentEvent into srcos namespace, creating an inconsistent mix.

Approach (no loss of intent):

1. Keep legacy schemas stable

• Preserve existing *.schema.json files and their legacy $id values.

2. Add canonical wrappers

• Add *.json wrapper schemas with canonical $id under https://schemas.srcos.ai/v2/control-plane/<Type>.json.
• Each wrapper uses allOf with a single $ref to the legacy schema.

3. Document the policy

• Update schemas/control-plane/README.md to define the two-layer identity model and list canonical wrapper filenames.

Wrappers added:

• ExperienceProfile.json
• IsolationProfile.json
• ReleaseSet.json
• BootReleaseSet.json
• EnrollmentToken.json
• Fingerprint.json
• MeshSkill.json
• SkillExecutionEvent.json
• IncidentEvent.json

Notes:

• Legacy refs continue to work.
• New work should reference canonical wrappers.
• A future major/minor may fully normalize legacy $id values once downstream consumers migrate.