[Doc][Misc] Restructure tutorial documentation (#6501)

### What this PR does / why we need it?

This PR refactors the tutorial documentation by restructuring it into
three categories: Models, Features, and Hardware. This improves the
organization and navigation of the tutorials, making it easier for users
to find relevant information.

- The single `tutorials/index.md` is split into three separate index
files:
  - `docs/source/tutorials/models/index.md`
  - `docs/source/tutorials/features/index.md`
  - `docs/source/tutorials/hardwares/index.md`
- Existing tutorial markdown files have been moved into their respective
new subdirectories (`models/`, `features/`, `hardwares/`).
- The main `index.md` has been updated to link to these new tutorial
sections.

This change makes the documentation structure more logical and scalable
for future additions.

### Does this PR introduce _any_ user-facing change?

Yes, this PR changes the structure and URLs of the tutorial
documentation pages. Users following old links to tutorials will
encounter broken links. It is recommended to set up redirects if the
documentation framework supports them.

### How was this patch tested?

These are documentation-only changes. The documentation should be built
and reviewed locally to ensure all links are correct and the pages
render as expected.

- vLLM version: v0.15.0
- vLLM main: https://github.com/vllm-project/vllm/commit/v0.15.0

Signed-off-by: wangxiyuan <wangxiyuan1007@gmail.com>

docs/source/quick_start.md

@@ -114,7 +114,7 @@ prompts = [
 ]
 sampling_params = SamplingParams(temperature=0.8, top_p=0.95)
 # The first run will take about 3-5 mins (10 MB/s) to download models
-llm = LLM(model="Qwen/Qwen2.5-0.5B-Instruct")
+llm = LLM(model="Qwen/Qwen3-0.6B")
 
 outputs = llm.generate(prompts, sampling_params)
 
@@ -130,13 +130,13 @@ for output in outputs:
 
 vLLM can also be deployed as a server that implements the OpenAI API protocol. Run
 the following command to start the vLLM server with the
-[Qwen/Qwen2.5-0.5B-Instruct](https://huggingface.co/Qwen/Qwen2.5-0.5B-Instruct) model:
+[Qwen/Qwen3-0.6B](https://huggingface.co/Qwen/Qwen3-0.6B) model:
 
 <!-- tests/e2e/doctest/001-quickstart-test.sh should be considered updating as well -->
 
 ```bash
 # Deploy vLLM server (The first run will take about 3-5 mins (10 MB/s) to download models)
-vllm serve Qwen/Qwen2.5-0.5B-Instruct &
+vllm serve Qwen/Qwen3-0.6B &
 ```
 
 If you see a log as below:
@@ -166,7 +166,7 @@ You can also query the model with input prompts:
 curl http://localhost:8000/v1/completions \
     -H "Content-Type: application/json" \
     -d '{
-        "model": "Qwen/Qwen2.5-0.5B-Instruct",
+        "model": "Qwen/Qwen3-0.6B",
         "prompt": "Beijing is a",
         "max_completion_tokens": 5,
         "temperature": 0