feat: Add start-dev.bat and improve app.py error reporting

Added Windows-optimized launcher:
- start-dev.bat: Simple batch file using npm run dev
  - Automatically kills processes on ports 3001 and 5173
  - Uses concurrently to run both services
  - Single window, simpler than Python launcher
  - Recommended for Windows users

Improved app.py:
- Better error output capture and display
- Increased wait time to 3 seconds
- Shows last 500 characters of error output

Windows users now have 3 options:
1. start-dev.bat (simplest - recommended)
2. python app.py (advanced with port management)
3. npm run dev (manual)

🤖 Generated with Claude Code
Co-Authored-By: Claude <noreply@anthropic.com>

start-dev.bat

@@ -0,0 +1,33 @@
+@echo off
+REM 5 Why Root Cause Analyzer - Simple Dev Launcher
+REM Uses npm dev which runs both services with concurrently
+
+echo.
+echo ======================================================================
+echo   5 Why Root Cause Analyzer - v1.0.0
+echo   Starting Development Servers...
+echo ======================================================================
+echo.
+
+REM Kill any existing processes on ports 3001 and 5173
+echo Cleaning up ports...
+for /f "tokens=5" %%a in ('netstat -ano ^| findstr :3001 ^| findstr LISTENING') do taskkill /F /PID %%a 2>nul
+for /f "tokens=5" %%a in ('netstat -ano ^| findstr :5173 ^| findstr LISTENING') do taskkill /F /PID %%a 2>nul
+
+echo.
+echo Starting services with npm dev...
+echo.
+echo Access Points:
+echo   Frontend: http://localhost:5173
+echo   Backend:  http://localhost:3001
+echo.
+echo Test Accounts:
+echo   Admin: admin@example.com / Admin@123456
+echo   User1: user001@example.com / User@123456
+echo   User2: user002@example.com / User@123456
+echo.
+echo Press Ctrl+C to stop all services
+echo ======================================================================
+echo.
+
+npm run dev