fix(kimaki): stop normalizing agent overrides

[chubes4]

Summary

• rely on Kimaki 0.13 missing-agent fallback instead of rewriting --agent flags to build
• keep generic Kimaki agent guidance in the filtered prompt and refresh effective-prompt snapshots
• register the real kimaki binary for CLI-channel dispatch while leaving datamachine-kimaki as a thin compatibility delegate

Closes #144.

Verification

• Verified upstream Kimaki main / 0.13.0 source: resolveValidatedAgentPreference() logs missing agents and returns agentPreference: undefined, falling back to the default agent.
• tests/datamachine-kimaki-adapter.sh
• node tests/effective-prompt/run.mjs
• tests/bridge-render.sh
• bash -n bridges/kimaki.sh bridges/kimaki/bin/datamachine-kimaki tests/datamachine-kimaki-adapter.sh
• git diff --check

AI assistance

• AI assistance: Yes
• Tool(s): OpenCode (GPT-5.5)
• Used for: Drafted the code/test/docs updates, refreshed snapshots, and ran targeted verification; Chris remains responsible for review and merge.

[chubes4]

Superseded by integration PR #162, which combines the Kimaki 0.13 cleanup work and resolves the overlapping bridge/test conflicts.