Fix Windows deployment scripts for missing Python dependencies

Issues fixed:
1. Build-Frontend.ps1: Add verification that requirements.txt is included in deployment package
   - Prevents incomplete packages that cause ModuleNotFoundError on server
   - Throws error if critical files are missing before package is transferred

2. Deploy-ROA2WEB.ps1: Auto-detect first deployment and force install dependencies
   - Automatically sets ForceInstallDependencies=true on first deployment
   - Add -ForceInstallDependencies parameter for manual override
   - Better error handling and validation for pip install
   - Shows clear error messages with manual recovery instructions

This fixes the "ModuleNotFoundError: No module named 'httpx'" error that occurred
when deploying to Windows Server without explicitly forcing dependency installation.

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

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

deployment/windows/scripts/Build-Frontend.ps1

@@ -281,6 +281,15 @@ function Copy-BackendFiles {
 
     $backendFiles = Get-ChildItem -Path $DestPath -Recurse -File
     Write-Success "Copied $(($backendFiles).Count) backend files"
+
+    # Verify critical files are present
+    $requirementsTxt = Join-Path $DestPath "requirements.txt"
+    if (-not (Test-Path $requirementsTxt)) {
+        Write-Error "CRITICAL: requirements.txt not found in backend package!"
+        Write-Host "    Expected: $requirementsTxt" -ForegroundColor Red
+        throw "Backend package incomplete - missing requirements.txt"
+    }
+    Write-Success "Verified: requirements.txt present"
 }
 
 function New-DeploymentPackage {