## Bug Description

When creating an MCP server via `POST /v1/mcp/server` with `auth_type: "bearer_token"` and `credentials.auth_value`, the `auth_value` is **not persisted** to the database. The server is created successfully (HTTP 201), but `GET /v1/mcp/server` returns `credentials: null` or `credentials: {}`.

The `encrypt_credentials()` function in `db.py` **does** handle `auth_value` encryption correctly, so the issue is in the create path — `credentials` are not being passed to the DB write.

## Environment

- **LiteLLM Version**: Reproduced on v1.86.0, v1.86.2, and v1.88.0rc1 - **OS**: macOS (ARM64) - **Database**: PostgreSQL - **Transport**: HTTP MCP server with bearer token auth

## Steps to Reproduce

```bash # 1. Create an HTTP MCP server with bearer token credentials curl -s -X POST http://localhost:4001/v1/mcp/server \ -H "Authorization: Bearer <MASTER_KEY>" \ -H "Content-Type: application/json" \ -d '{ "server_name": "test_auth_server", "transport": "http", "url": "https://example.com/mcp", "auth_type": "bearer_token", "credentials": { "auth_value": "os.environ/SOME_API_KEY" }, "mcp_access_groups": ["test"] }' # Returns 201 wi…