Sort feature settings alphabetically within sections

What does this MR do and why?

The two GitLab Duo "Model selection" pages render feature-setting rows in whatever order the GraphQL API returns them. As sections grow — "GitLab Duo Agent Platform" now has eight rows — that ordering gets hard to scan.

This MR sorts rows within each section alphabetically by feature title.

• ee/app/assets/javascripts/ai/model_selection/feature_settings.vue (group/namespace-level page): plain alphabetical sort by title.
• ee/app/assets/javascripts/ai/instance_model_selection/feature_settings/components/feature_settings.vue (instance/Admin area page): already groups rows by release state (GA, then Beta, then Experiment) to show a maturity badge next to each name. That grouping stays as the primary sort key; title is now the tiebreaker within each group.

No backend, GraphQL, or database changes. No new user-facing strings. No feature flag — this is a presentational ordering change with no rollout risk.

Jest specs updated for both components: the namespace spec adds a case feeding deliberately unsorted data and asserts alphabetised output; the instance spec's per-section assertions now compare titles instead of internal feature keys.

References

Closes #627116 (closed)

Parent epic: gitlab-org#19786

Supersedes an earlier, stale draft: !236770 (closed)

Screenshots or screen recordings

Before	After

Ordering change for the "GitLab Duo Agent Platform" section on the instance page:

#	Before	After
1	Agents & flows	Agentic Code Review
2	Duo Developer	Agents & flows
3	Agentic Code Review	Duo Developer
4	Secret Vulnerability False Positive Detection	Secret Vulnerability False Positive Detection
5	SAST Vulnerability False Positive Detection (Beta)	Resolve Dependency Bump Breaking Changes (Beta)
6	SAST Vulnerability Resolution (Beta)	SAST Vulnerability False Positive Detection (Beta)
7	Security Review (Beta)	SAST Vulnerability Resolution (Beta)
8	Resolve Dependency Bump Breaking Changes (Beta)	Security Review (Beta)

How to set up and validate locally

1. Check out this branch.
2. Visit the instance page: Admin area > GitLab Duo > Model selection, on the "AI-native features" tab.
3. Confirm each section's rows read alphabetically by title, and that Beta-badged rows still sit below the GA rows and are alphabetised among themselves.
4. Visit a group's Settings > GitLab Duo > Model selection.
5. Confirm each section there is plainly alphabetical by title.

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