Hide Install Coder Desktop / Install CLI items in UserDropdown when already installed

Bắt đầu bằng việc xem xét UserDropdownContent và PR #28244, nơi đã giới thiệu các mục cài đặt. Điều tra các tín hiệu phía trình duyệt được đề xuất để phát hiện việc cài đặt Coder Desktop và CLI, sau đó xác định xem có tín hiệu đáng tin cậy hay không. Công việc được xem là hoàn tất khi các mục tương ứng được ẩn nếu việc phát hiện là đáng tin cậy, hoặc khi các phát hiện được ghi lại nếu không đáng tin cậy.

Background

Follow-up from #28244 (DEVEX-722), which added an Install Coder Desktop item to the UserDropdown, sitting above the existing Install CLI item.

During review, Christin suggested that we only surface these install options when the respective tool has not been installed yet. It was intentionally left out of scope for that PR, and we agreed to track it as a follow-up.

Proposal

Hide the Install Coder Desktop and Install CLI items in UserDropdownContent when the user already has the respective tool installed.

Considerations / open questions

• There is no reliable browser-side API to detect whether a native desktop application is installed. Some ideas to explore:
  • Custom URL scheme / protocol handler probing (e.g., attempt to open a coder:// deep link and detect success/failure).
  • A signal sent from Coder Desktop itself (e.g., a local endpoint, a cookie, or a header) that the web app can read.
  • Detecting a running local agent/session initiated by Coder Desktop.
• For the CLI, detection is even trickier from the browser; we may need to rely on a heuristic (e.g., "has the user ever downloaded the CLI or authenticated a session via CLI on this deployment").
• UX: decide whether to hide the item entirely, collapse it into a submenu, or show it with a "installed" state.

Acceptance criteria (draft)

• Investigate feasible detection mechanisms for Coder Desktop (and, if practical, the CLI).
• If a reliable signal is available, hide the corresponding Install … item in the UserDropdown when the tool is installed.
• If no reliable signal is available, document the findings and close the issue.

References

• PR: https://github.com/coder/coder/pull/28244
• Review comment: https://github.com/coder/coder/pull/28244#pullrequestreview-4960748169
• Linear: DEVEX-722

Created on behalf of @jakehwll