Windows: v1.0.66 fails to start stdio MCP servers when command is a .bat/.cmd with args (regression from 1.0.65)

## Summary

On Windows, **v1.0.66 fails to start any stdio MCP server whose `command` is a `.bat`/`.cmd` file and is registered with one or more `args`.** The child process dies immediately with cmd.exe's `The syntax of the command is incorrect.` and the client reports `connection closed: initialize response`. The exact same servers worked in **v1.0.65**.

This looks like a regression in how the Windows `.bat`/`.cmd` spawn path builds/quotes the command line (consistent with the post‑CVE‑2024‑27980 Node hardening for batch files).

## Environment

- Copilot CLI: **1.0.66-1** (broken) — worked on **1.0.65**
- OS: Windows 11 (`10.0.26200`), x64
- Install: WinGet (`GitHub.Copilot`)
- Bundled Node: `v24.16.0`

## What fails vs. what works

Given these MCP registrations:

| `command` | `args` | Result on 1.0.66 |
|---|---|---|
| `foo.bat` | `["serve"]` | ❌ fails: `The syntax of the command is incorrect.` |
| `foo.bat` | `[]` (no args) | ✅ works |
| `python.exe` (a real `.exe`) | `["-m","foo","serve"]` | ✅ works |
| http server | n/a | ✅ works |

So the failure is specific to **`.bat`/`.cmd` command + non-empty `args`**. Removing the argument (or pointing `command` at a real `.exe`) avoids it.

## Logs

```
[ERROR] Starting MCP client for dashpilot with command: d:\LRPBot\dashpilot.bat and args: serve
[ERROR] [mcp server dashpilot stderr] The syntax of the command is incorrect.
[ERROR] Failed to start MCP client for dashpilot: Error: failed to initialize MCP client: connection closed: initialize response
```

In the same session, every `.bat … serve` server failed identically (5 of them), while one `.bat` registered with empty args and all `http` servers started fine. On 1.0.65, all of the same `.bat … serve` servers started normally.

## Minimal reproduction

1. Create `C:\tmp\echo.bat`:
```bat
@echo off
echo got arg: %~1 1>&2
```
2. Register it with an argument:
```
copilot mcp add repro -- "C:\tmp\echo.bat" serve
```
3. Launch `copilot` → the `repro` server fails to start with `The syntax of the command is incorrect.`
4. Re-register **without** the argument and the spawn no longer errors:
```
copilot mcp remove repro
copilot mcp add repro -- "C:\tmp\echo.bat"
```

(For a server that actually completes MCP initialization, wrap any stdio MCP server in a `.bat` and register it `-- "wrapper.bat" serve` vs `-- "wrapper.bat"`.)

## Expected

A `.bat`/`.cmd` MCP `command` with `args` should be spawned with a correctly quoted command line (as it was in 1.0.65), so the server initializes normally.

## Workaround

Register the `.bat` with **no args** (have the batch file default to its serve subcommand), or point `command` directly at the underlying `.exe` (e.g. the venv `python.exe`) with the args.

Beginne damit, den Fehler über den Startpfad des MCP-stdio-Servers mit den bereitgestellten echo.bat-Befehlen zu reproduzieren, und vergleiche anschließend das Verhalten zwischen den Versionen 1.0.65 und 1.0.66. Die Arbeit ist abgeschlossen, wenn .bat- und .cmd-Befehle mit nicht leeren Argumenten die MCP-Initialisierung unter Windows starten und abschließen, während die bestehenden Fälle ohne Argumente und mit ausführbaren Dateien weiterhin funktionieren.

Vom Indexierungsmodell aus dem Issue-Text verfasst.