Fix dm-agent-sync OpenCode agent mutation

[chubes4]

Summary

• Narrow dm-agent-sync.ts to only recompose Data Machine memory at OpenCode session config time.
• Stop querying all Data Machine agents, registering them into OpenCode config, or writing agent.build.prompt / agent.plan.prompt.
• Update tests and docs to describe selected-agent instructions plus memory recomposition.

Closes #147.

Verification

• node tests/dm-agent-sync.mjs
• bash tests/repair-opencode-json.sh
• ./tests/opencode-local-plugin-path.sh
• ./tests/bridge-render.sh
• ./tests/datamachine-kimaki-adapter.sh
• ./tests/opencode-wrapper-removal.sh
• bash -c 'set -e; fail=0; while IFS= read -r -d "" f; do if ! bash -n "$f"; then echo "FAIL: $f"; fail=1; fi; done < <(find . -type f -name "*.sh" -not -path "./.git/*" -print0); exit "$fail"'

AI assistance

• AI assistance: Yes
• Tool(s): OpenCode (GPT-5.5)
• Used for: Drafted the code, test, and documentation updates for Chris to review and verify.

[chubes4]

Superseded by integration PR #162, which combines the Kimaki 0.13 cleanup work and resolves the overlapping bridge/test conflicts.