Point Duo Chat Orbit "Leave feedback" link to master epic

What does this MR do and why?

Follow-up to !262193 (merged). The Leave feedback link in the Duo Chat Orbit popover still pointed to closed work items:

• Team members: gitlab-org#21994 (closed) ("Orbit Customer Zero", closed 2026-09-19)
• Everyone else: #598867 (closed) ("Feedback: Orbit", closed 2026-06-04)

This MR replaces both with the open umbrella epic gitlab-org#22266 ("Orbit Feedback (Master)"), matching the Orbit dashboard. The team-member branch is removed, so is_gitlab_team_member is no longer read here.

Changes

• ee/app/assets/javascripts/ai/duo_agentic_chat/components/orbit_toggle.vue: single ORBIT_FEEDBACK_URL constant, exposed via $options.orbitFeedbackUrl; removed the feedbackUrl computed.
• ee/spec/frontend/ai/duo_agentic_chat/components/orbit_toggle_spec.js: replaced the two href tests with one for the master epic.

How to set up and validate locally

1. Open Duo Chat with Orbit available and enabled.
2. Click the Orbit button, then Leave feedback.
3. Confirm it opens gitlab-org#22266.

MR acceptance checklist

• I have evaluated the MR acceptance checklist for this MR.