Draft: SDLC Context Agent - Add frontend toggle for Vulnerability Context Analysis project setting

What does this MR do and why?

Adds the frontend UI toggle for the Vulnerability Context Analysis project-level setting (https://gitlab.com/gitlab-org/gitlab/-/work_items/611376).

This is the frontend part of the SDLC Context Agent Phase 4 implementation. The backend setting was added in !249617 (merged).

References

• https://gitlab.com/gitlab-org/gitlab/-/work_items/611376
• Backend MR: !249617 (merged)

Screenshots or screen recordings

N/A — this adds a toggle to the existing GitLab Duo project settings page, following the same visual pattern as the SAST FP detection toggle.

Before	After
No Vulnerability Context Analysis toggle	Toggle visible for Ultimate users

How to set up and validate locally

1. Navigate to a project's GitLab Duo settings page
2. Ensure the project has an Ultimate license (ultimateFeaturesAvailable: true)
3. Verify the "Turn on Vulnerability Context Analysis" toggle appears below the SAST VR Workflow toggle
4. Toggle it and save — the duo_vulnerability_context_analysis_enabled attribute should be submitted

MR acceptance checklist

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