Add stdio plugin host foundation #2048

Job	Run time
rustfmt	26s
clippy	1m 40s
cargo-check (protocol)	35s
cargo-check (orchestrator-cli)	1m 44s
cargo-check (llm-cli-wrapper)	35s
cargo-check (orchestrator-web-server)	1m 30s
cargo-check (orchestrator-core)	49s
cargo-check (agent-runner)	41s
cargo-check (orchestrator-web-contracts)	31s
cargo-check (orchestrator-web-api)	1m 8s
smoke-help	0s
	9m 39s

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