refactor(werkbank): extract soft-PLC provisioning + ICS probe into werkbank-exec (WB-04a)

Prep for the Werkbank Docker executor (sharang/werkbank#5): the dynamic-execution
logic has to be usable by the runner (a separate repo), so lift it out of the
agent into a shared crate.

New crate `werkbank-exec` (git-mv preserves history):
- src/ics/*        — the read-only industrial-protocol probe (Modbus/OPC-UA/
                     EtherNet-IP/portscan), moved verbatim.
- src/plc/*        — ephemeral soft-PLC provisioning (DockerSoftPlc), the OpenPLC
                     program-load client, and provision_and_test/extract_program.
- src/error.rs     — a crate-local ExecError, replacing the agent's AgentError.
- src/fingerprint.rs — compute_fingerprint (copied from the agent's dedup).
Depends only on compliance-core + compliance-dast, so the runner can pull it
without the agent's server stack.

compliance-agent consumes it:
- AgentError gains `Exec(#[from] werkbank_exec::ExecError)`.
- The orchestrator's ICS-probe + provision-and-test call sites point at
  werkbank_exec::{ics,plc}; the old pipeline::ics and plc::runtime modules are
  removed (the static PLC scanner stays).
- CI clippy-checks + tests the new crate.

Pure move + rename — no behaviour change. 27 moved tests pass in the new crate;
283 agent lib tests pass; clippy + fmt clean.

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

werkbank-exec/Cargo.toml

@@ -0,0 +1,23 @@
+[package]
+name = "werkbank-exec"
+version = "0.1.0"
+edition = "2021"
+description = "Shared dynamic-execution logic: soft-PLC provisioning + industrial-protocol probing, used by the compliance agent and the Werkbank runner."
+
+[lints]
+workspace = true
+
+[dependencies]
+compliance-core = { workspace = true }
+compliance-dast = { path = "../compliance-dast" }
+tokio = { workspace = true }
+reqwest = { workspace = true }
+uuid = { workspace = true }
+regex = { workspace = true }
+secrecy = { workspace = true }
+sha2 = { workspace = true }
+hex = { workspace = true }
+tracing = { workspace = true }
+thiserror = { workspace = true }
+walkdir = "2"
+futures-util = "0.3"