Bug: CLI produces no stdout in child process (Start-Process) on Windows — blocks headless automation

## Bug: Copilot CLI v1.0.18 produces no stdout/stderr when launched via `Start-Process` on Windows

### Summary

When launching `copilot` as a child process via PowerShell's `Start-Process` on Windows, the CLI produces **zero bytes** of output to both stdout and stderr, even though it runs successfully in an interactive shell. This is a regression — the same `Start-Process` approach captured output correctly on **March 31, 2026** but stopped working by **April 5, 2026** (likely after a CLI update).

### Environment

- **Copilot CLI version:** 1.0.18
- **OS:** Windows 11 (10.0.26200)
- **PowerShell:** 7.x (pwsh)
- **Node.js:** v22.21.0
- **Install method:** WinGet + npm global

### Reproduction Steps

**Works** (interactive shell, output captured):
```powershell
cd C:\path\to\git-repo
$output = & copilot -p "Say hello" --yolo --no-ask-user -s --no-color --disable-builtin-mcps 2>&1
# $output contains the response ✅
```

**Fails** (child process via Start-Process, 0 bytes):
```powershell
# Method 1: Start-Process with redirect (0 bytes)
Start-Process -FilePath copilot.cmd -ArgumentList '-p "Say hello" --yolo --no-ask-user -s --no-color --disable-builtin-mcps' -NoNewWindow -RedirectStandardOutput out.txt -RedirectStandardError err.txt -Wait
# out.txt = 0 bytes, err.txt = 0 bytes

# Method 2: Launcher script with > redirect (0 bytes)
# launcher.ps1 contains: & copilot.cmd -p "Say hello" --yolo -s --no-color --disable-builtin-mcps > out.txt 2> err.txt
Start-Process -FilePath pwsh -ArgumentList "-NoProfile -ExecutionPolicy Bypass -File launcher.ps1" -NoNewWindow -Wait
# out.txt = 0 bytes

# Method 3: Launcher script with pipeline Out-File (0 bytes in child process)
# launcher.ps1 contains: & copilot.cmd -p "Say hello" --yolo -s --no-color --disable-builtin-mcps 2>&1 | Out-File out.txt
Start-Process -FilePath pwsh -ArgumentList "-NoProfile -ExecutionPolicy Bypass -File launcher.ps1" -NoNewWindow -Wait
# out.txt = 0 bytes (but works when run directly in current shell!)

# Method 4: Start-Transcript (captures PS header only, not copilot output)
# launcher.ps1 contains: Start-Transcript out.txt; & copilot.cmd ...; Stop-Transcript
# out.txt = PS version header only, no copilot output
```

### Expected Behavior

All four methods should capture copilot's response text. Method 1 (`Start-Process -RedirectStandardOutput`) worked correctly on March 31 with the same codebase.

### Actual Behavior

Copilot CLI appears to write output to the Windows console handle directly rather than stdout. This means:

1. **Interactive shell:** `& copilot ... 2>&1` captures output via PowerShell's pipeline (which intercepts console writes in the current session)
2. **Child process:** The child `pwsh` process gets a different console session, and copilot's console writes go to a handle that no redirection mechanism can capture

### Evidence of Regression

Dispatch logs from **March 31** using the same `Start-Process -RedirectStandardOutput` approach show captured output (924–2311 bytes). Dispatch logs from **April 5** show 0 bytes across all attempts. The only change between sessions was a copilot CLI update.

### Impact

This blocks all headless/automated use of Copilot CLI on Windows, including:
- Dispatching work to child squad repos via `Start-Process`
- Running Copilot CLI in CI/CD pipelines
- Any automation that launches copilot as a background process and captures results

### Workaround

The only working approach is invoking copilot in the **current** interactive shell session using `& copilot ... 2>&1`. This doesn't work for background/async automation because it blocks the parent session.

### Suggested Fix

Copilot CLI should write to stdout (file descriptor 1) rather than directly to the Windows console handle (`WriteConsoleW` / `WriteFile` to `CONOUT$`). This would make all standard redirection mechanisms work (`>`, `Start-Process -RedirectStandardOutput`, pipes, `Start-Transcript`).

Alternatively, provide a `--output-file ` flag that writes the session transcript to a file, bypassing the console entirely.