Adds a stdlib HTTP control plane that wraps scripts/switch.sh so a harness
can POST /switch and block until the new model is serving. Introduces no new
orchestration logic — switch.sh stays the single source of truth (registry
lookup, down/up, readiness).
- tools/model-switch/server.py: GET /healthz|/status|/models, POST /switch
({slug}|{model}); registry-validated; /health readiness (works with or
without VLLM_API_KEY); single-flight lock; refuses to start unauthenticated
on a non-loopback bind.
- scripts/systemd/club3090-model-switch.service: host daemon unit.
- scripts/tests/test-model-switch.sh: hermetic HTTP/auth/validation contract.
- docs/EXAMPLES.md, .env.example: usage + config.
Mirrors the existing stdlib HTTP style (services/studio/*); zero new deps.
Experimental/opt-in per the repo's staging convention.