feat(cli,format): deterministic JSON envelope with plumb_version, run… #102

Job	Run time
Preflight (fmt, clippy, check, agents-md)	40s
Size guard (<25 MiB)	2m 4s
MSRV (1.95)	27s
Determinism	39s
Docs (build, no deploy)	34s
Test (ubuntu-latest)	1m 16s
cargo-deny	31s
Test (macos-latest)	1m 15s
Test (windows-latest)	3m 24s
Coverage	1m 24s
	12m 14s

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