Fix Windows setup sequencing wrapper quoting (#8806)

* fix(setup): correct Windows sequencing wrapper quoting

* test(setup): preserve spaced Windows batch paths

* refactor(setup): dedupe PowerShell encoder, clarify wrapCmd comment

Route the Windows setup-sequencing and Hermes startup planners through the
shared renderer-safe encodePowerShellCommand instead of two verbatim btoa
copies, and make that shared encoder renderer-safe (Buffer is unavailable in
the sandboxed renderer where both planners also run). Reword the wrapCmd
comment so it describes the current single-outer-quote behavior instead of the
old quote-doubling bug.

* test(setup): cover Windows metacharacter paths

* fix(setup): keep Windows runner paths out of cmd source

* test(setup): preserve Windows setup failures

* docs(setup): explain safe cmd path handoff

---------

Co-authored-by: OrcaWin <alpha-eng@stably.ai>
Co-authored-by: OrcaWin <293788423+OrcaWin@users.noreply.github.com>

src/shared/powershell-command-encoding.ts

@@ -1,3 +1,11 @@
 export function encodePowerShellCommand(command: string): string {
-  return Buffer.from(command, 'utf16le').toString('base64')
+  // Why: some callers (setup sequencing, Hermes startup) run in the sandboxed
+  // renderer where Node's Buffer is unavailable, so encode the UTF-16LE bytes
+  // PowerShell's -EncodedCommand expects using only renderer-safe globals.
+  let bytes = ''
+  for (let index = 0; index < command.length; index += 1) {
+    const code = command.charCodeAt(index)
+    bytes += String.fromCharCode(code & 0xff, code >>> 8)
+  }
+  return btoa(bytes)
 }