feat(wfe-yaml): add deno_core JS/TS executor with sandboxed permissions

Secure JavaScript/TypeScript execution in workflow steps via deno_core,
behind the `deno` feature flag.

Security features:
- Per-step permission system: net host allowlist, filesystem read/write
  path restrictions, env var allowlist, subprocess spawn control
- V8 heap limits (64MB default) prevent memory exhaustion
- Execution timeout with V8 isolate termination for sync infinite loops
- Path traversal detection blocks ../ escape attempts
- Dynamic import rejection unless explicitly enabled

Workflow I/O ops:
- inputs() — read workflow data as JSON
- output(key, value) — set step outputs
- log(message) — structured tracing

Architecture:
- JsRuntime runs on dedicated thread (V8 is !Send)
- PermissionChecker enforced on every I/O op via OpState
- DenoStep implements StepBody, integrates with existing compiler
- Step type dispatch: "shell" or "deno" in YAML

34 new tests (12 permission unit, 3 config, 2 runtime, 18 integration).

wfe-yaml/src/executors/deno/ops/mod.rs

@@ -0,0 +1,3 @@
+pub mod workflow;
+
+pub use workflow::{StepMeta, StepOutputs, WorkflowInputs};

wfe-yaml/src/executors/deno/ops/workflow.rs

@@ -0,0 +1,52 @@
+use std::collections::HashMap;
+
+use deno_core::op2;
+use deno_core::OpState;
+
+/// Workflow data available to the script via `inputs()`.
+pub struct WorkflowInputs {
+    pub data: serde_json::Value,
+}
+
+/// Accumulates key/value outputs set by the script via `output(key, value)`.
+pub struct StepOutputs {
+    pub map: HashMap<String, serde_json::Value>,
+}
+
+/// Metadata about the currently executing step.
+pub struct StepMeta {
+    pub name: String,
+}
+
+/// Returns the workflow input data to JavaScript.
+#[op2]
+#[serde]
+pub fn op_inputs(state: &mut OpState) -> serde_json::Value {
+    let inputs = state.borrow::<WorkflowInputs>();
+    inputs.data.clone()
+}
+
+/// Stores a key/value pair in the step outputs.
+#[op2]
+pub fn op_output(
+    state: &mut OpState,
+    #[string] key: String,
+    #[serde] value: serde_json::Value,
+) {
+    let outputs = state.borrow_mut::<StepOutputs>();
+    outputs.map.insert(key, value);
+}
+
+/// Logs a message via the tracing crate.
+#[op2(fast)]
+pub fn op_log(state: &mut OpState, #[string] msg: String) {
+    let name = state.borrow::<StepMeta>().name.clone();
+    tracing::info!(step = %name, "{}", msg);
+}
+
+deno_core::extension!(
+    wfe_ops,
+    ops = [op_inputs, op_output, op_log],
+    esm_entry_point = "ext:wfe/bootstrap.js",
+    esm = ["ext:wfe/bootstrap.js" = "src/executors/deno/js/bootstrap.js"],
+);