Update UI copy to use "GitLab Orbit" instead of standalone "Orbit"

What does this MR do and why?

Updates user-facing UI strings across the GitLab Orbit dashboard to use "GitLab Orbit" instead of standalone "Orbit", per legal guidance that "GitLab Orbit" must always be used in composite.

Raised in gitlab-org/orbit/knowledge-graph!2026 (closed)#note_3553603145 by @dfrhodes, confirmed by @fneill in gitlab-org/orbit/knowledge-graph!2026 (closed)#note_3555914179.

Strings updated:

• Nav item title (ee/lib/sidebars/your_work/menus/orbit_menu.rb)
• Breadcrumb (ee/app/views/dashboard/orbit/show.html.haml)
• Page <h1> (app.vue, orbit_empty_state.vue)
• Empty state body copy (orbit_empty_state.vue, orbit_explore_empty_state.vue)
• Connect section title, subtitle, and Duo integration strings (connect_section.vue)
• Setup guide modal strings (orbit_explore_empty_state.vue)

Not changed: Internal identifiers — Ruby method names, JS variable names, CSS classes, event tracking names, i18n namespace keys (Orbit|) — are all unchanged.

Testing

• Verify nav item shows "GitLab Orbit" in the left sidebar
• Verify page <h1> shows "GitLab Orbit"
• Verify empty state body copy uses "GitLab Orbit"
• Verify connect section title/subtitle use "GitLab Orbit"