[CI]Add CI summary log (#7202)

### What this PR does / why we need it?
This PR adds a new CI log summarizer, `ci_log_summary.py`, and wires it
into unit-test and e2e workflows so failed jobs publish a structured
failure summary to the GitHub step summary.
Examples:
- `python3 .github/workflows/scripts/ci_log_summary.py --log-file
/tmp/unit-test.log --mode ut --step-name "Unit test"`
- `python3 .github/workflows/scripts/ci_log_summary.py --run-id
23127187822 --format json`

A maintenance note is added to `ci_utils.py` to clarify that the `START`
/ `PASSED` / `FAILED (exit code X)` log lines are parsed by
`ci_log_summary.py`, so any future format changes must be coordinated
with the corresponding summarizer regexes.

🤖 Generated with [Codex]<noreply@openai.com>
- vLLM version: v0.16.0
- vLLM main:
4034c3d32e
---------
Signed-off-by: Meihan-chen <jcccx.cmh@gmail.com>
Signed-off-by: meihanc <jcccx.cmh@gmail.com>
Co-authored-by: Codex <noreply@openai.com>

docs/source/developer_guide/contribution/testing.md

@@ -285,6 +285,23 @@ For running nightly multi-node test cases locally, refer to the `Running Locally
         model.save_pretrained(DIST_MODEL_PATH)
         ```
 
+### View CI log summary in GitHub Actions
+
+After a CI job finishes, you can open the corresponding GitHub Actions job page and check the
+`Summary` tab to view the generated CI log summary.
+
+![GitHub Actions CI log summary](../../assets/ci_log_summary.png)
+
+The summary is intended to help developers triage failures more quickly. It may include:
+
+- failed test files
+- failed test cases
+- distinct root-cause errors
+- short error context extracted from the job log
+
+This summary is generated from the job log by
+`/.github/workflows/scripts/ci_log_summary_v2.py` for unit-test and e2e workflows.
+
 ### Run doctest
 
 vllm-ascend provides a `vllm-ascend/tests/e2e/run_doctests.sh` command to run all doctests in the doc files.