fix(build): disable shell wrapper when passing custom environment

Root cause: When exec() uses shell: true (WIN32), the spawn helper wraps
commands in cmd.exe. Environment variables passed via env option are not
properly propagated from cmd.exe to subprocesses (python, ninja).

Debug output confirmed:
- ✅ VS variables exist in process.env
- ✅ env option passed with 221 variables
- ❌ configure.py subprocess can't see variables

Solution: Set shell: false when passing custom env on Windows. This calls
python/ninja directly without cmd.exe wrapper, ensuring environment variables
are inherited correctly.

Applied to:
- configure.py execution (line 1455)
- ninja build execution (line 1511)

This is the correct fix for the Windows smol build failure.

Author: jdalton

packages/node-smol-builder/scripts/build.mjs

@@ -1447,10 +1447,13 @@ async function main() {
   logger.log(`::group::Running ${WIN32 ? 'python configure.py' : './configure'}`)
 
   // On Windows, explicitly pass environment to subprocess.
+  // IMPORTANT: When passing custom env, we must disable shell wrapping (shell: false)
+  // because cmd.exe doesn't properly propagate environment variables to subprocesses.
   const execOptions = { cwd: NODE_DIR }
   if (WIN32) {
     execOptions.env = process.env
-    logger.log(`DEBUG: Passing env option with ${Object.keys(process.env).length} variables`)
+    execOptions.shell = false  // Critical: disable cmd.exe wrapper
+    logger.log(`DEBUG: Passing env with ${Object.keys(process.env).length} variables (shell: false)`)
   }
 
   await exec(configureCommand, configureArgs, execOptions)
@@ -1502,7 +1505,12 @@ async function main() {
     logger.log('::group::Compiling Node.js with Ninja (this will take a while...)')
 
     try {
-      await exec('ninja', ['-C', 'out/Release', `-j${CPU_COUNT}`], { cwd: NODE_DIR, env: process.env })
+      // On Windows, disable shell wrapper when passing env (same as configure.py).
+      const ninjaOptions = { cwd: NODE_DIR, env: process.env }
+      if (WIN32) {
+        ninjaOptions.shell = false
+      }
+      await exec('ninja', ['-C', 'out/Release', `-j${CPU_COUNT}`], ninjaOptions)
       logger.log('::endgroup::')
     } catch (e) {
       logger.log('::endgroup::')