feat(regex): add .NET regex validation via PowerShell and integrate into frontend

backend/scripts/validate.ps1

@@ -0,0 +1,73 @@
+#!/usr/bin/env pwsh
+# Validate a .NET regex pattern
+
+param(
+    [Parameter(Mandatory=$false)]
+    [string]$Pattern
+)
+
+# Set output encoding to UTF-8
+[Console]::OutputEncoding = [System.Text.Encoding]::UTF8
+$ErrorActionPreference = "Stop"
+
+# Read pattern from stdin if not provided as parameter
+if (-not $Pattern) {
+    $Pattern = [System.Console]::In.ReadToEnd()
+}
+
+# Ensure we have a pattern
+if ([string]::IsNullOrWhiteSpace($Pattern)) {
+    $result = @{
+        valid = $false
+        error = "No pattern provided"
+    }
+    Write-Output (ConvertTo-Json $result -Compress)
+    exit 0
+}
+
+try {
+    # Attempt to create a .NET Regex object with the pattern
+    # Using IgnoreCase option as per requirement
+    $regex = [System.Text.RegularExpressions.Regex]::new($Pattern, [System.Text.RegularExpressions.RegexOptions]::IgnoreCase)
+    
+    # If we get here, the pattern is valid
+    $result = @{
+        valid = $true
+        message = "Pattern is valid .NET regex"
+    }
+    
+    Write-Output (ConvertTo-Json $result -Compress)
+    exit 0
+}
+catch {
+    # Pattern is invalid, extract the meaningful part of the error message
+    $errorMessage = $_.Exception.Message
+    
+    # Try to extract just the useful part of .NET regex errors
+    if ($errorMessage -match "Invalid pattern '.*?' at offset (\d+)\. (.+)") {
+        $errorMessage = "At position $($matches[1]): $($matches[2])"
+    }
+    elseif ($errorMessage -match 'parsing ".*?" - (.+)') {
+        $errorMessage = $matches[1]
+    }
+    elseif ($errorMessage -match 'Exception calling .* with .* argument\(s\): "(.+)"') {
+        $innerError = $matches[1]
+        if ($innerError -match "Invalid pattern '.*?' at offset (\d+)\. (.+)") {
+            $errorMessage = "At position $($matches[1]): $($matches[2])"
+        }
+        else {
+            $errorMessage = $innerError
+        }
+    }
+    
+    # Remove any trailing quotes or periods followed by quotes
+    $errorMessage = $errorMessage -replace '\."$', '.' -replace '"$', ''
+    
+    $result = @{
+        valid = $false
+        error = $errorMessage
+    }
+    
+    Write-Output (ConvertTo-Json $result -Compress)
+    exit 0
+}