feat(debug): enable Python debug workflow and debug server integration

Adds an end-to-end Python debug workflow for the extension.
Includes a new prepare-debug.ps1 script and a VS Code task.
Extends the Python server and extension to coordinate a debug session and safe startup.

- Add prepare-debug.ps1 and a VS Code task to build the debug bundle
- Enable Python debug wiring in the server and tests
- Ensure a single stable Python debug session during startup

.vscode/prepare-debug.ps1

@@ -0,0 +1,57 @@
+param(
+    [Parameter(Mandatory = $true)]
+    [string]$WorkspaceRoot,
+
+    [Parameter(Mandatory = $true)]
+    [string]$DebugRoot
+)
+
+Set-StrictMode -Version Latest
+$ErrorActionPreference = "Stop"
+
+function ConvertFrom-ExtendedWindowsPath {
+    param([string]$Path)
+
+    if ($Path.StartsWith("\\?\UNC\", [System.StringComparison]::OrdinalIgnoreCase)) {
+        return "\\" + $Path.Substring(8)
+    }
+    if ($Path.StartsWith("\\?\", [System.StringComparison]::OrdinalIgnoreCase)) {
+        return $Path.Substring(4)
+    }
+    return $Path
+}
+
+$workspacePath = ConvertFrom-ExtendedWindowsPath $WorkspaceRoot
+$workspaceItem = Get-Item -LiteralPath $workspacePath
+if (-not $workspaceItem.PSIsContainer) {
+    throw "Workspace root is not a directory: $workspacePath"
+}
+$workspacePath = $workspaceItem.FullName
+
+$debugPath = ConvertFrom-ExtendedWindowsPath $DebugRoot
+$tempPath = [System.IO.Path]::GetFullPath([System.IO.Path]::GetTempPath()).TrimEnd("\")
+$debugParent = [System.IO.Path]::GetFullPath((Split-Path -Parent $debugPath)).TrimEnd("\")
+if (-not $debugParent.Equals($tempPath, [System.StringComparison]::OrdinalIgnoreCase)) {
+    throw "Debug alias must be located directly below the user temp directory: $debugPath"
+}
+
+if (Test-Path -LiteralPath $debugPath) {
+    $debugItem = Get-Item -LiteralPath $debugPath -Force
+    if ($debugItem.LinkType -ne "Junction") {
+        throw "Debug alias exists but is not a junction: $debugPath"
+    }
+
+    $currentTarget = (Get-Item -LiteralPath $debugItem.Target).FullName
+    if (-not $currentTarget.Equals($workspacePath, [System.StringComparison]::OrdinalIgnoreCase)) {
+        # Removing a junction removes only the link, never the target directory.
+        Remove-Item -LiteralPath $debugPath -Force
+    }
+}
+
+if (-not (Test-Path -LiteralPath $debugPath)) {
+    New-Item -ItemType Junction -Path $debugPath -Target $workspacePath | Out-Null
+}
+
+Write-Output "Debug extension path: $debugPath -> $workspacePath"
+& npm.cmd --prefix $workspacePath run compile:debug
+exit $LASTEXITCODE