fix(onboarding): actually probe shell PATH for node; stop returning Electron's bundled version

The `checkNodeInstalled` IPC handler was hardcoded to
`{ installed: true, version: process.version }`. That meant:

1. The NodeCheckStep in onboarding ALWAYS passed, regardless of what
   was actually on the user's machine.
2. The "Node.js vX.Y installed" success banner showed the **Electron
   runtime's** bundled Node version, not the one the agent's bash
   tool will invoke. A user with no shell Node saw "Node.js v22.x
   installed" and moved on, then every agent bash call that executed
   `node -e 'fetch(...)'` (the pattern the API prompt-builder strongly
   recommends in `api-docs/header.en.md`) crashed at runtime.

Replaced the stub with an `execFile("node", ["--version"])` probe that
runs in the same PATH the bash tool will later inherit. Added a 3s
timeout so a hung PATH entry doesn't stall onboarding. On failure the
handler returns `{ installed: false, version: null }` — the existing
NodeCheckStep already renders the platform-specific install
instructions (brew / winget / nvm) in that case.

No UI change; the fake-pass was the bug. Covers the onboarding audit
item about misleading health checks.

src/main/ipc-core-admin-handlers.ts

@@ -1,3 +1,4 @@
+import { execFile } from "node:child_process";
 import {
   IPC_CHANNELS,
   companyInputSchema,
@@ -11,6 +12,27 @@ import { validateConnectorConfigurationModel, validateConnectorModelSelection }
 import { reconcileExecutionModeChange } from "./execution-mode-reconciler";
 import { fail, ok, type RegisterCoreHandlersDependencies } from "./ipc-core-common";
 
+/**
+ * Probe the user's shell PATH for a `node` binary. The onboarding Node
+ * check uses this to decide whether agents will be able to run the
+ * "Node.js fetch()" snippets the API prompt-builder emits. Returns the
+ * shell `node --version` output on success; never surfaces the raw
+ * `process.version` (that is Electron's bundled Node, not what the
+ * agent's bash tool will actually invoke).
+ */
+function probeShellNode(timeoutMs = 3000): Promise<{ installed: boolean; version: string | null }> {
+  return new Promise((resolve) => {
+    execFile("node", ["--version"], { timeout: timeoutMs }, (error, stdout) => {
+      if (error) {
+        resolve({ installed: false, version: null });
+        return;
+      }
+      const version = stdout.trim();
+      resolve({ installed: version.length > 0, version: version.length > 0 ? version : null });
+    });
+  });
+}
+
 export function registerCoreAdminHandlers({
   registerHandle,
   db,
@@ -108,7 +130,7 @@ export function registerCoreAdminHandlers({
   });
 
   registerHandle(IPC_CHANNELS.checkNodeInstalled, async () => {
-    return ok({ installed: true, version: process.version });
+    return ok(await probeShellNode());
   });
 
   registerHandle(IPC_CHANNELS.openTerminalCommand, async (_event, payload) => {