fix: robust node.js version parsing in installers

Improved Node.js version check logic to handle prefixed version strings and avoid brittle cut commands. Verified with multiple version formats including v24.11.1.

install-windows.ps1

@@ -179,10 +179,18 @@ function Install-Dependencies {
     # Check Node.js
     $nodeCmd = Get-Command node -ErrorAction SilentlyContinue
     if ($nodeCmd) {
-        $version = & node --version
-        Write-ColorOutput "Node.js found: $version" -Type Success
+        $nodeFullVersion = & node --version
+        $nodeMajorVersion = ($nodeFullVersion -replace '^v', '') -split '\.' | Select-Object -First 1
+        
+        if ([int]$nodeMajorVersion -lt 18) {
+            Write-ColorOutput "Node.js version $nodeMajorVersion is too old! Node.js 18 or newer is required." -Type Error
+            exit 1
+        }
+        
+        Write-ColorOutput "Node.js found: $nodeFullVersion" -Type Success
     } else {
-        Write-ColorOutput "Node.js not found. Some features may not work." -Type Warning
+        Write-ColorOutput "Node.js not found. Node.js 18 or newer is required to install Claude Code." -Type Error
+        exit 1
     }
 
     # Check Git