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>

Cargo.lock

@@ -699,6 +699,7 @@ dependencies = [
  "urlencoding",
  "uuid",
  "walkdir",
+ "werkbank-exec",
  "zip",
 ]
 
@@ -6714,6 +6715,25 @@ dependencies = [
  "rustls-pki-types",
 ]
 
+[[package]]
+name = "werkbank-exec"
+version = "0.1.0"
+dependencies = [
+ "compliance-core",
+ "compliance-dast",
+ "futures-util",
+ "hex",
+ "regex",
+ "reqwest",
+ "secrecy",
+ "sha2",
+ "thiserror 2.0.18",
+ "tokio",
+ "tracing",
+ "uuid",
+ "walkdir",
+]
+
 [[package]]
 name = "which"
 version = "6.0.3"