Fix organization scoping in REST API project list endpoints

What does this MR do and why?

Fix organization scoping in the REST API project list endpoints.

ProjectsFinder#by_organization reads params[:organization] to filter projects by organization, but load_projects in lib/api/projects.rb was passing current_organization: (wrong key) instead of organization:. This caused the organization filter to be silently ignored, so GET /projects and GET /users/:user_id/projects returned projects from all organizations instead of only the current one.

This is the same defect already fixed for the Explore controller in !251487 (merged).

References

• Closes #620655
• Related: !251487 (merged) (Explore controller fix, mirrored here)
• Related: !246815 (merged)

Screenshots or screen recordings

backend-only fix, no UI changes.

How to set up and validate locally

1. In a Rails console, set Current.organization to a specific organization.
2. Call GET /api/v4/projects. Before this fix, projects from other organizations were returned. After the fix, only projects in the current organization are returned.

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