## Bug Report

### Description

When editing an existing MCP server with OAuth2 M2M (`client_credentials`) auth, the **Edit Settings → Tool Configuration** panel shows:

> **Unable to load tools** > Failed to connect to MCP server. Check proxy logs for details.

### Root Cause

The edit form populates `formValues` from the server record returned by `GET /v1/mcp/server/<id>`. For OAuth2 servers, `credentials` is always `null` in API responses (encrypted at rest, redacted for security). The UI then calls `POST /mcp-rest/test/tools/list` with the form values — but since `client_id` and `client_secret` are missing, the test endpoint cannot fetch an OAuth2 token and the connection fails.

**Code path:** 1. `mcp_tool_configuration.tsx` → `useTestMCPConnection` hook → `testMCPToolsListRequest` 2. Backend: `rest_endpoints.py` `_execute_with_mcp_client()` — `_extract_credentials()` returns `(None, None, None)` 3. `has_client_credentials` is `False` → no M2M token fetch → connection fails with generic error

### Expected Behavior

For existing M2M servers, the Tool Configuration panel should be able to load tools without requiring credentials to be re-entered. Options: 1. Use the stored (enc…