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 {

deployment/windows/scripts/Deploy-ROA2WEB.ps1

@@ -27,6 +27,9 @@
 .PARAMETER UpdateFrontend
     Update frontend files (default: true)
 
+.PARAMETER ForceInstallDependencies
+    Force reinstall all Python dependencies even if requirements.txt hasn't changed (default: false)
+
 .EXAMPLE
     cd C:\Deploy\ROA2WEB\scripts
     .\Deploy-ROA2WEB.ps1
@@ -36,6 +39,10 @@
     .\Deploy-ROA2WEB.ps1 -UpdateBackend -UpdateFrontend:$false
     Update only backend files
 
+.EXAMPLE
+    .\Deploy-ROA2WEB.ps1 -ForceInstallDependencies $true
+    Update files and force reinstall all Python dependencies
+
 .NOTES
     Author: ROA2WEB Team
     Requires: PowerShell 5.1+, Administrator privileges
@@ -48,7 +55,8 @@ param(
     [bool]$BackupEnabled = $true,
     [bool]$RestartService = $true,
     [bool]$UpdateBackend = $true,
-    [bool]$UpdateFrontend = $true
+    [bool]$UpdateFrontend = $true,
+    [bool]$ForceInstallDependencies = $false
 )
 
 $ErrorActionPreference = "Stop"
@@ -242,27 +250,51 @@ function Update-BackendFiles {
 
         Write-Success "Backend files updated"
 
-        # Check if requirements.txt changed
+        # Check if requirements.txt changed or if force install is requested
         $sourceReq = Join-Path $sourceBackend "requirements.txt"
         $destReq = Join-Path $Config.BackendPath "requirements.txt"
 
         if (Test-Path $sourceReq) {
             $sourceHash = (Get-FileHash $sourceReq).Hash
             $destHash = if (Test-Path $destReq) { (Get-FileHash $destReq).Hash } else { "" }
+            $requirementsChanged = $sourceHash -ne $destHash
 
-            if ($sourceHash -ne $destHash) {
+            if ($requirementsChanged -or $ForceInstallDependencies) {
+                if ($ForceInstallDependencies) {
+                    Write-Step "Force installing Python dependencies..."
+                } else {
                     Write-Step "Requirements changed, updating Python dependencies..."
+                }
+
                 Copy-Item -Path $sourceReq -Destination $destReq -Force
 
                 try {
+                    # Verify Python is available
+                    $pythonCmd = Get-Command python -ErrorAction SilentlyContinue
+                    if (-not $pythonCmd) {
+                        Write-Error "Python not found in PATH. Please ensure Python 3.11+ is installed."
+                        throw "Python not found"
+                    }
+
+                    Write-Host "    Installing/upgrading dependencies from: $destReq" -ForegroundColor Gray
                     & python -m pip install -r $destReq --upgrade
-                    Write-Success "Python dependencies updated"
+
+                    if ($LASTEXITCODE -eq 0) {
+                        Write-Success "Python dependencies installed successfully"
+                    } else {
+                        Write-Error "pip install failed with exit code: $LASTEXITCODE"
+                        throw "Dependency installation failed"
+                    }
                 } catch {
                     Write-Error "Failed to update Python dependencies: $_"
+                    Write-Warning "Try running manually: python -m pip install -r $destReq"
+                    throw
                 }
             } else {
                 Write-Success "Python dependencies unchanged"
             }
+        } else {
+            Write-Warning "requirements.txt not found in source package"
         }
     } catch {
         Write-Error "Failed to update backend files: $_"
@@ -466,6 +498,13 @@ function Main {
     }
     Write-Success "Installation path exists"
 
+    # Check if this is first deployment (no backend files yet)
+    $isFirstDeployment = -not (Test-Path (Join-Path $Config.BackendPath "app"))
+    if ($isFirstDeployment) {
+        Write-Warning "First deployment detected - will install all dependencies"
+        $script:ForceInstallDependencies = $true
+    }
+
     try {
         # Deployment steps
         $backupPath = Backup-CurrentDeployment