feat: enhance serving functionality and add comprehensive examples

- Improve API server with better error handling and response formatting
- Enhance CLI with additional options for DiT stages and configuration
- Add comprehensive examples in examples/basic/ including:
  - API client with health checks and text generation
  - Docker setup and usage examples
  - Simple usage patterns for different scenarios
- Add utility scripts for model downloading and Docker setup
- Update documentation with implementation details and testing guidelines
- Fix configuration validation issues in OmniLLM
- Improve stage configuration handling for AR and DiT stages
- Add proper error handling and fallback mechanisms

Tested with Qwen3-0.6B model:
- Server starts successfully on port 8000
- Health and info endpoints working correctly
- Text generation with various parameters functioning
- API client examples working as expected
- CLI help and configuration options working properly

examples/basic/README.md

@@ -0,0 +1,76 @@
+# Basic vLLM-omni Examples
+
+This directory contains simple examples demonstrating how to use vLLM-omni for text generation.
+
+## Examples
+
+### 1. `simple_usage.py` - Direct Library Usage
+
+Demonstrates how to use vLLM-omni directly in your Python code:
+
+```bash
+# Run the example
+python simple_usage.py
+```
+
+**Features:**
+- Synchronous text generation
+- Asynchronous text generation  
+- Multi-prompt processing
+- Shows both text output and token information
+
+### 2. `api_client.py` - API Server Usage
+
+Demonstrates how to interact with the vLLM-omni API server:
+
+```bash
+# First, start the server
+vllm serve Qwen/Qwen3-0.6B --omni --port 8000
+
+# Then run the client (in another terminal)
+python api_client.py
+```
+
+**Features:**
+- Health check
+- Text generation via HTTP API
+- Multiple prompt types
+- Full response structure inspection
+
+## Quick Start
+
+1. **Install vLLM-omni:**
+   ```bash
+   pip install -e .
+   ```
+
+2. **Run direct usage example:**
+   ```bash
+   cd examples/basic
+   python simple_usage.py
+   ```
+
+3. **Run API server example:**
+   ```bash
+   # Terminal 1: Start server
+   vllm serve Qwen/Qwen3-0.6B --omni --port 8000
+   
+   # Terminal 2: Run client
+   cd examples/basic
+   python api_client.py
+   ```
+
+## Expected Output
+
+The examples will show:
+- ✅ Generated text responses
+- ✅ Token counts and completion status
+- ✅ Stage processing information
+- ✅ Error handling
+
+## Requirements
+
+- Python 3.8+
+- vLLM-omni installed
+- For API examples: HTTP server running
+