Simplify provider registration authorization

[ziaxzulu]

Summary

• expose only anonymous proof of work and bearer-token authorization
• remove bootstrap-grant client configuration and wire fields
• rename the canonical context binding to authorizationId
• document and enforce exclusive per-instance durable state ownership

Validation

• TMPDIR=/home/zulu/.cache/codex-tmp/registration-token-network ./gradlew :warden-signalling:test
• schema and fixture copied byte-for-byte from the Warden generator output