chore(deps): bump vllm from 0.25.1 to 0.26.0 in /backend/python/vllm (#11402)

* chore(deps): bump vllm from 0.25.1 to 0.26.0 in /backend/python/vllm

Bumps [vllm](https://github.com/vllm-project/vllm) from 0.25.1 to 0.26.0.
- [Release notes](https://github.com/vllm-project/vllm/releases)
- [Changelog](https://github.com/vllm-project/vllm/blob/main/RELEASE.md)
- [Commits](https://github.com/vllm-project/vllm/compare/v0.25.1...v0.26.0)

---
updated-dependencies:
- dependency-name: vllm
  dependency-version: 0.26.0
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

Signed-off-by: dependabot[bot] <support@github.com>

* fix(vllm): pin Intel source build to release

Build the Intel XPU backend from vLLM 0.26.0 instead of the moving main branch, and use the Triton XPU version required by that release's torch 2.12 dependency.

Assisted-by: Codex:gpt-5 [systematic-debugging]

---------

Signed-off-by: dependabot[bot] <support@github.com>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>
Co-authored-by: localai-org-maint-bot <306269227+localai-org-maint-bot@users.noreply.github.com>

backend/python/vllm/requirements-l4t13-after.txt

@@ -9,4 +9,4 @@
 # memory architecture crash deterministically with an empty "Engine core init
 # failed" set (mudler/LocalAI#10722). Leaving this unpinned let the L4T image
 # drift onto whatever wheel was latest at build time.
-vllm==0.25.1
+vllm==0.26.0