Codex task: implement release-ready model routing policy CLI skeleton

[mdheller]

Mission

Bootstrap model-router as a release-ready CLI skeleton for governed model/service routing.

This issue is designed for a Codex agent. Keep the change bounded and open a PR.

Required commands

model-router --version
model-router doctor
model-router self-test
model-router emit-evidence
model-router route --task <task> --privacy <policy>
model-router explain <route-id>
model-router test examples/route-policy.json

Required behavior

• Deterministic routing simulation without external model calls.
• Inputs include task, privacy posture, latency preference, cost preference, and deployment mode.
• Output includes selected route, fallback route, policy rationale, and evidence metadata.
• Missing runtime services are reported as not-yet-wired.

Required repo additions

• CLI entrypoint
• route policy example
• route decision example
• validator/tests
• Makefile targets: build, test, validate, dist, release-dry-run

Acceptance criteria

• make validate passes.
• model-router route --task summarize --privacy local-first emits deterministic JSON.
• model-router doctor, self-test, and emit-evidence work without external services.
• README documents Prophet CLI delegation: prophet model route.

Do not

• Do not call hosted APIs.
• Do not vendor model artifacts.
• Do not hardcode fake availability as real production state.