R2: remove AU-51 bearer layer from planning/spec-writing model composites; delete retired @1 templates (dbc5efc6)

The @2 templates use CP-side verdict/WIA decompose and never read the bearer.
Triggers already pin version 2.

Claude-Session: https://claude.ai/code/session_01N218bERyNeLhbLmDRDvbWF

harnesses/composites/spec-writing-sonnet-repo/v1/harness.yaml

@@ -8,6 +8,3 @@ layers:
   - context: anthropic-cloud-paul-oauth/v1
   - context: gitea-ssh/v1
   - context: agent-repo/v1
-  # AU-51/AU-51b: this composite backs scope-decompose-sonnet@1, which
-  # calls back POST /v1/work-items/{id}/decompose — needs a credential.
-  - context: cp-service-token/v1