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/Cargo.toml

@@ -4,6 +4,10 @@ version.workspace = true
 edition.workspace = true
 description = "YAML workflow definitions for WFE"
 
+[features]
+default = []
+deno = ["deno_core", "url"]
+
 [dependencies]
 wfe-core = { workspace = true }
 serde = { workspace = true }
@@ -14,9 +18,12 @@ tokio = { workspace = true }
 thiserror = { workspace = true }
 tracing = { workspace = true }
 regex = { workspace = true }
+deno_core = { workspace = true, optional = true }
+url = { workspace = true, optional = true }
 
 [dev-dependencies]
 pretty_assertions = { workspace = true }
 tokio = { workspace = true, features = ["test-util", "process"] }
+tokio-util = "0.7"
 wfe-core = { workspace = true, features = ["test-support"] }
 wfe = { path = "../wfe" }