feat(cmd/crucible): add simulate subcommand to trace events through an IR

[joshua-temple]

Closes #175. Follow-up tracked in #183 (CEL-from-context guard evaluation).

What

crucible simulate <ir.json> fires an ordered event sequence through a machine assembled from the IR and prints the per-event step trace (from/to state, outcome, emitted effects) and the final state — for debugging and CI snapshot tests.

crucible simulate machine.json -events "checkout,paid" -guard hasItems=true -guard isPaid=true
crucible simulate machine.json -events-file scenario.json -format json

• Events: -events (comma list) or -events-file (a bare ["a","b"] array or a conformance.Scenario object); exactly one required.
• Guards: a headless IR has no real behavior, so guards return seeded verdicts — -guard name=bool (repeatable); unseeded guards default to false. Actions/reducers/services are no-ops.
• -initial overrides the IR's declared start state; -format text|json.

Design notes

• Reuses state/conformance.RunAgainst (no reimplemented Fire loop).
• Exit codes: a guard-blocked or invalid transition is a legitimate observable trace → exit 0; an unknown event (*conformance.ErrUnknownEvent) or a real replay/action failure → exit 1; arg/validation errors → exit 2. The result error is classified with errors.As so blocked-but-valid traces stay distinct from failures.
• JSON shape mirrors conformance.TraceStep (scalar states, real outcome enum values).

Verification

• go build / go vet / go test (86 pass) / golangci-lint (0 issues) — all green in cmd/crucible.
• End-to-end against the binary (12 assertions): seeded guards reach the final state; unseeded guards block (outcome GuardFailed, exit 0); -events-file, -initial, JSON output, unknown-event→exit 1, and all validation errors→exit 2 behave as specified.