Route the update version check through an archcore.ai proxy

[ivklgn]

Problem

archcore update's version check calls https://api.github.com/repos/…/releases/latest directly (internal/update/update.go), which is subject to unauthenticated rate limits that can make the check fail for some users.

Expected result

The release check is routed through an archcore.ai proxy endpoint, with a transparent fallback to GitHub on proxy outage. The client change is small once the endpoint exists.

Impact

Makes the update check reliable regardless of a user's GitHub rate-limit state.

Scope

• Make the release-check base URL configurable (default to the proxy once available).
• Fall back to the current GitHub URL on non-200 / network error.
• Cover both paths with httptest.

Files: internal/update/update.go (+ tests)

Acceptance: the version check prefers the proxy and transparently falls back to GitHub.

Status: blocked — requires the server-side proxy endpoint (out of this repo) first.