fix(pkg): support worker-backed tools in single exe

pkg stores application files in a virtual filesystem, and its
worker_threads hook discovers worker entry points only when they are passed
as filesystem strings. Convert the code-runtime entry with fileURLToPath()
and return the workflow built entry as a string while retaining its
source-mode data URL bootstrap.

Emit worker entry bundles as CommonJS .cjs files. pkg executes a VFS-backed
string-path worker through Module._compile, so an ESM-only entry can be
present in the executable yet still fail when launched. Keep the public hosts
ESM, adapt worker startup accordingly, and align exports, package file lists,
workspace constraints, documentation, and built-worker tests with the actual
artifact format.

Expand the custom-config executable smoke to load the Code Mode and workflow
plugins and script real run_code and zero-agent workflow calls. Require both
tools to return 42 from workers launched inside the pkg VFS, turning worker
support from an asset-presence assumption into an end-to-end runtime
contract.

Update the implemented RFC and verification gates to describe and exercise
the supported built-worker path. This adds no tool or JSON-RPC protocol shape;
it fixes how existing worker-backed capabilities are located and executed in
the single-file distribution.

packages/workflow/workflow-workerthread/src/host.ts

@@ -43,6 +43,7 @@
 
 import { Worker } from 'node:worker_threads'
 import type { WorkerOptions } from 'node:worker_threads'
+import { fileURLToPath } from 'node:url'
 import type { Context } from 'cordis'
 import type { Agent } from '@deepseek-ai/dsh-agent'
 import { assertNever } from '@deepseek-ai/dsh-llm'
@@ -87,12 +88,12 @@ interface ChildRecord {
  * AMBIENT channel only — an escapee still holds process-wide privileges
  * like fs access (the README's trust premise stands).
  * @param init - the run payload, passed as `workerData`.
- * @returns the entry URL and the Worker options to spawn it with.
+ * @returns the entry path or URL and the Worker options to spawn it with.
  */
-function resolveWorkerSpawn(init: WorkerInit): { entry: URL; options: WorkerOptions } {
+function resolveWorkerSpawn(init: WorkerInit): { entry: string | URL; options: WorkerOptions } {
   /* v8 ignore next 3 -- the built-output arm: tests always run unbuilt (src/); the built-worker e2e exercises this shape for real */
   if (!import.meta.url.endsWith('.ts')) {
-    return { entry: new URL('./worker.js', import.meta.url), options: { workerData: init, env: {}, execArgv: [] } }
+    return { entry: fileURLToPath(new URL('./worker.cjs', import.meta.url)), options: { workerData: init, env: {}, execArgv: [] } }
   }
   // Resolve tsx lazily: only the unbuilt shape executes this arm, so a built
   // consumer never needs the dev-only loader installed. A JavaScript entry is