Request: Create unified sglang/vllm images to use both AIBrix KVCache and routing features

### 🚀 Feature Description and Motivation

Currently AIBrix KVCache and routing tests are using separate images. Using a single image to reduce maintenance overhead and provide cleaner dev/test vehicle.

### Use Case

Used for both dev & testing.

### Proposed Solution

_No response_

No files, tests, or image entry points are identified. Start by locating the separate AIBrix KVCache and routing sglang/vllm image definitions and their dev/test consumers; done means one shared image supports both workflows and the existing tests run against it.

Written by the indexing model from the issue text.