Add Windows service host and system tray controller

start_backend.ps1

@@ -16,7 +16,22 @@ function Test-EnvVarLine {
 }
 
 if (-not (Get-Command python -ErrorAction SilentlyContinue)) {
-    throw "Python was not found in PATH. Install Python 3.11+ and retry."
+    $venvPython = Join-Path $scriptDir ".venv\Scripts\python.exe"
+    if (-not (Test-Path -LiteralPath $venvPython)) {
+        throw "Python was not found in PATH and .venv\\Scripts\\python.exe is missing. Install Python 3.11+ or create .venv first."
+    }
+}
+
+$pythonExe = $null
+$venvPython = Join-Path $scriptDir ".venv\Scripts\python.exe"
+if (Test-Path -LiteralPath $venvPython) {
+    $pythonExe = $venvPython
+} else {
+    $pythonCmd = Get-Command python -ErrorAction SilentlyContinue
+    if ($null -eq $pythonCmd) {
+        throw "Python was not found in PATH. Install Python 3.11+ or create .venv first."
+    }
+    $pythonExe = $pythonCmd.Source
 }
 
 $envFile = Join-Path $scriptDir ".env"
@@ -32,4 +47,4 @@ if (-not (Test-Path -LiteralPath $envFile)) {
 }
 
 Write-Host "Starting ScreenJob backend on configured host/port..." -ForegroundColor Cyan
-python main.py server
+& $pythonExe main.py server