Add WinPython support to the System Python manager (#1369)

fixes:
#1251

PET can discover WinPython environments, but the extension was silently
dropping them because `WinPython` was not a recognized
`NativePythonEnvironmentKind`. WinPython is a portable Windows Python
distribution that belongs under the existing System Python manager
alongside `WindowsRegistry`, `WindowsStore`, and `GlobalPaths`.

## Changes

- **`nativePythonFinder.ts`** — Add `winpython = 'WinPython'` to the
`NativePythonEnvironmentKind` enum to match the value emitted by PET's
`pet-winpython` crate.
- **`managers/builtin/utils.ts`** — Add
`NativePythonEnvironmentKind.winpython` to the `refreshPythons`
allowlist so WinPython environments surface through the System Python
manager.

WinPython falls through to the `default` branch in `getKindName()`, so
it displays as `Python <version>` — consistent with other undecorated
system Pythons.

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Author: Copilot

src/managers/builtin/utils.ts

@@ -125,6 +125,7 @@ export async function refreshPythons(
                         NativePythonEnvironmentKind.macXCode,
                         NativePythonEnvironmentKind.windowsRegistry,
                         NativePythonEnvironmentKind.windowsStore,
+                        NativePythonEnvironmentKind.winpython,
                     ].includes(e.kind)),
         );
     envs.forEach((env) => {

src/managers/common/nativePythonFinder.ts

@@ -140,6 +140,7 @@ export enum NativePythonEnvironmentKind {
     virtualEnvWrapper = 'VirtualEnvWrapper',
     windowsStore = 'WindowsStore',
     windowsRegistry = 'WindowsRegistry',
+    winpython = 'WinPython',
 }
 
 export interface NativePythonFinder extends Disposable {