docs: add analysis on ghost process and launcher cleanup

docs/GHOST_PROCESS_FIX_SUMMARY.md

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+# Quick Fix Summary: Ghost Process Issue
+
+## Problem
+Task Manager freezed after launcher runs due to accumulating ghost PowerShell processes.
+
+## Root Cause
+**File:** `backend/utils/platformUtils.js`
+
+Two functions used `execSync()` to run PowerShell commands:
+- `detectGpuWindows()` (GPU detection at startup & game launch)
+- `getSystemTypeWindows()` (system type detection)
+
+`execSync()` on Windows spawns PowerShell processes that don't properly terminate → accumulate over time → freeze Task Manager.
+
+## Solution Applied
+
+### Changed From (❌ Wrong):
+```javascript
+output = execSync(
+  'powershell -NoProfile -ExecutionPolicy Bypass -Command "Get-CimInstance..."',
+  { encoding: 'utf8', stdio: ['ignore', 'pipe', 'ignore'] }
+);
+```
+
+### Changed To (✅ Correct):
+```javascript
+const result = spawnSync('powershell.exe', [
+  '-NoProfile',
+  '-ExecutionPolicy', 'Bypass',
+  '-Command',
+  'Get-CimInstance...'
+], {
+  encoding: 'utf8',
+  timeout: 5000,  // 5 second timeout - processes killed if hung
+  stdio: ['ignore', 'pipe', 'ignore'],
+  windowsHide: true
+});
+```
+
+## What Changed
+
+| Aspect | Before | After |
+|--------|--------|-------|
+| **Method** | `execSync()` → shell string | `spawnSync()` → argument array |
+| **Process spawn** | Via cmd.exe → powershell.exe | Direct powershell.exe |
+| **Timeout** | None (can hang indefinitely) | 5 seconds (processes auto-killed) |
+| **Process cleanup** | Hit or miss | Guaranteed |
+| **Ghost processes** | ❌ Accumulate over time | ✅ Always terminate |
+| **Performance** | Slower (shell parsing) | Faster (direct spawn) |
+
+## Why This Works
+
+1. **spawnSync directly spawns PowerShell** without intermediate cmd.exe
+2. **timeout: 5000** forcibly kills any hung process after 5 seconds
+3. **windowsHide: true** prevents window flashing and improves cleanup
+4. **Node.js has better control** over process lifecycle with spawnSync
+
+## Impact
+
+- ✅ No more ghost PowerShell processes
+- ✅ Task Manager stays responsive  
+- ✅ Launcher performance improved
+- ✅ Game launch unaffected (still works the same)
+- ✅ All fallback methods preserved (Get-WmiObject, wmic)
+
+## Files Changed
+
+Only one file modified: **`backend/utils/platformUtils.js`**
+- Import added for `spawnSync`
+- Two functions refactored with new approach
+- All error handling preserved
+
+## Testing
+
+After applying fix, verify no ghost processes appear in Task Manager:
+
+```
+Before launch: PowerShell processes = 0 or 1
+During launch: PowerShell processes = 0 or 1
+After game closes: PowerShell processes = 0 or 1
+```
+
+If processes keep accumulating, check Task Manager → Details tab → look for powershell.exe entries.