chore(charts): sync nebari-llm-serving v0.1.3-signingtest.1 from nebari-dev/llm-serving-pack

[dcmcand]

Automated chart sync

Field	Value
Chart	nebari-llm-serving
Version	0.1.3-signingtest.1
Source repository	nebari-dev/llm-serving-pack
Source ref	test/signing-integration
Triggered by	workflow_dispatch at 3a94a9d7d026fe57507840faeecb8b011dc3b1fd

---

Merging this PR will trigger the
Release Helm Charts
workflow, which will:

1. Run helm package on the updated chart.
2. Merge the new package into index.yaml (preserving existing chart timestamps).
3. Publish the chart archive and updated index to the
   Nebari Helm Repository.

Note: This PR was opened automatically. Review the chart diff before merging.

To refresh it:

• New upstream release: push the release in the source repository, and this
  branch is force-updated automatically by the upstream sync workflow.
• Branch fell behind main (e.g., Chart.yaml conflict because a sibling
  sync PR merged first): comment /sync-rebase on this PR. A maintainer-gated
  workflow rebases the branch onto current main, resolving the
  version / appVersion clash automatically.

[dcmcand]

Closing: this PR synced the signing-integration TEST chart (nebari-llm-serving-0.1.3-signingtest.1), which is not for publication. Real OCI-chart signing is tracked in #64.