fix: Windows support & cross-platform architecture

Major fixes for Windows portable version:

1. **Fixed critical bugs:**
   - Replace Unix /dev/null with Windows nul in all .bat files
   - Unified config path to data/.openclaw/openclaw.json
   - Fixed cross-platform node_modules compatibility issue

2. **Implemented separated core directories:**
   - app/core-mac/ for Mac dependencies
   - app/core-win/ for Windows dependencies
   - Prevents cross-platform file system conflicts
   - Shared data/ directory for configs and memory

3. **Enhanced setup.sh:**
   - Now downloads both Mac and Windows Node.js runtimes
   - Ensures U-Claw works on both platforms after setup

4. **Added diagnostic tools:**
   - Windows-Diagnose.bat for troubleshooting
   - Mac-Diagnose.command for troubleshooting
   - Auto-generates diagnostic-log.txt

5. **Improved user experience:**
   - Added Welcome.html - Simple 3-step guide in Chinese
   - All scripts updated to use platform-specific core directories
   - Better error messages and user guidance

Files modified:
- portable/Windows-Start.bat: Use core-win, fix syntax
- portable/Windows-Menu.bat: Use core-win, fix syntax
- portable/Mac-Start.command: Use core-mac
- portable/Mac-Menu.command: Use core-mac
- portable/setup.sh: Download both platforms, use core-mac

Files added:
- portable/Windows-Diagnose.bat: Diagnostic tool
- portable/Mac-Diagnose.command: Diagnostic tool
- portable/Welcome.html: User-friendly welcome page

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

portable/Windows-Menu.bat

@@ -3,7 +3,7 @@ chcp 65001 >nul 2>&1
 title U-Claw Menu
 
 set "UCLAW_DIR=%~dp0"
-set "CORE_DIR=%UCLAW_DIR%app\core"
+set "CORE_DIR=%UCLAW_DIR%app\core-win"
 set "DATA_DIR=%UCLAW_DIR%data"
 set "STATE_DIR=%DATA_DIR%\.openclaw"
 set "NODE_DIR=%UCLAW_DIR%app\runtime\node-win-x64"