feat(werkbank): job/result contract in compliance-core (WB-01)

The shared, dependency-free vocabulary the control plane and the Werkbank
execution runner agree on: Job (declarative — TOML on disk, JSON on the wire),
JobType (plc-provision/qemu-boot/dast/pentest), Executor (shell/docker/k8s),
JobStatus lifecycle, InputRef (blob/url — the artifact resolves on the runner,
never through the control plane), JobRuntime, JobCollect, and JobResult (reusing
Finding/DastFinding/SbomEntry so the runner produces exactly what the control
plane persists).

Lives in a mongodb/axum-feature-free module so the runner can depend on
compliance-core without the server stack (verified: cargo check -p
compliance-core --no-default-features). Tests round-trip through JSON and parse
the exact plc-provision + qemu-boot TOML from the Werkbank design doc.

First story of the Werkbank epic (sharang/werkbank#1); implements
sharang/werkbank#2.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

compliance-core/Cargo.toml

@@ -50,3 +50,7 @@ axum = { version = "0.8", optional = true }
 jsonwebtoken = { version = "9", optional = true }
 reqwest = { workspace = true, optional = true }
 tokio = { workspace = true, optional = true }
+
+[dev-dependencies]
+# Parse the declarative TOML job specs in the Werkbank contract tests.
+toml = "0.8"