chore: remove dead opencode docs MCP

[xnoto]

Summary

Removes the retired opencode-docs MCP from the global OpenCode configuration, its permission allowlist, and the agent guidance that routed work to it. OpenCode configuration guidance now points to the checked-in schema and repository validation.

Fixes #

N/A

Type of change

• Refactor / cleanup

Validation

• Required pull-request checks pass — pending CI; no local checks were run.
• Generated or centrally distributed files were regenerated by their owning automation, not hand-edited — none.

Impact and rollout

The global opencode-docs server and permission namespace are removed. Project overlays and the gateway/client configurations are updated in coordinated PRs. After merge, workstation clients must be reloaded; no service restart or deployment was performed.

Safety and secrets

• Contains no plaintext secrets, decrypted SOPS values, state files, kubeconfigs, tokens, or private endpoints
• No local OpenTofu init/plan/apply/destroy/import/state operations were run or claimed — plans come from pull-request checks
• Breaking or irreversible effects are described above with rollback notes — restoring the removed config entries reverts this source-only change

Authored with an AI agent; independent code and security reviews were requested before PR creation.