Persistent OAuth client management for DevSpace MCP integration with ChatGPT across server restarts.

## Description

Environment: Windows 11 stable latest (26200.8655), PowerShell

When using DevSpace MCP with ChatGPT through a Cloudflare tunnel, the MCP works normally while the Node.js process keeps running. Disconnecting and reconnecting from ChatGPT does not break the connection.

However, after stopping the local server with Ctrl+C and starting it again with `npm run start`, ChatGPT can no longer reconnect. The OAuth page returns:

```json
{"error":"invalid_client","error_description":"Invalid client_id"}
```

## Steps to Reproduce

1. Start DevSpace with `npm run start`.

2. Add the MCP in ChatGPT and authenticate with the owner password.

3. Use the MCP to read local files successfully.

4. Disconnect and reconnect in ChatGPT; it still works.

5. Stop the local DevSpace process with Ctrl+C.

6. Run `npm run start` again.

7. Try reconnecting from ChatGPT.

8. The OAuth flow fails with `invalid_client`.

## Expected Behavior

After restarting the DevSpace server, an existing ChatGPT MCP connection should either reconnect successfully, or the server should handle re-registration cleanly.

## Actual Behavior

The server rejects the existing ChatGPT OAuth client with:

JSON

```json
{"error":"invalid_client","error_description":"Invalid client_id"}
```

## Possible Cause

From the source code, it looks like OAuth clients are stored in an in-memory `Map`. After the Node.js process restarts, the registered `client_id` is lost, while ChatGPT still tries to use the previously ...