Stop dm-agent-sync injecting Data Machine agent prompts

[chubes4]

Summary

• narrow dm-agent-sync.ts to only refresh Data Machine memory composition at OpenCode config load time
• remove runtime mutation of config.agent.build.prompt / config.agent.plan.prompt
• stop registering every Data Machine agent into OpenCode agent slots by default
• update tests/comments to document that Data Machine/channel routing owns identity

Fixes #141.

Tests

• node tests/dm-agent-sync.mjs
• bash tests/repair-opencode-json.sh
• bash tests/opencode-local-plugin-path.sh
• bash tests/post-upgrade-restore.sh
• bash tests/path-helpers.sh
• bash tests/opencode-wrapper-removal.sh
• bash tests/homeboy-components.sh
• bash tests/kimaki-session-helper-smoke.sh
• bash tests/datamachine-kimaki-adapter.sh
• bash tests/bridge-render.sh

Notes

• bash tests/runtime-signature.sh and bash tests/cli-channel-perms.sh currently stop on macOS/BSD awk: newline in string errors in unrelated runtime/bridge signature helpers before reaching this change area.

AI assistance

• AI assistance: Yes
• Tool(s): OpenCode (GPT-5.5)
• Used for: narrowed the OpenCode plugin, updated tests and comments, ran local verification, and prepared the PR for Chris to review.

[chubes4]

Superseded by integration PR #162, which combines the Kimaki 0.13 cleanup work and resolves the overlapping bridge/test conflicts.