feat: releases from GitHub first, then git.kebcloud.no; releases sets others

Updates and install.sh try the GitHub mirror, then git.kebcloud.no,
each with a short timeout, and download from the first server with the
release, checked against its checksums.txt. The releases config option
(and LAZYSECRETS_RELEASES for install.sh) lists other servers. The
release workflow copies each release to GitHub when GH_RELEASE_TOKEN is
set. The status pane's issues link points to GitHub.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

internal/ui/app/status.go

@@ -122,7 +122,9 @@ func (m Model) statusFields() []panes.Field {
 	repo := strings.TrimPrefix(update.DefaultRepo, "https://")
 	add(panes.Field{Label: "docs", Value: repo + "/…/docs", URL: update.DefaultRepo + "/src/branch/main/docs"})
 	add(panes.Field{Label: "source", Value: repo, URL: update.DefaultRepo})
-	add(panes.Field{Label: "issues", Value: repo + "/issues", URL: update.DefaultRepo + "/issues"})
+	// Issues are on the GitHub mirror.
+	github := strings.TrimPrefix(update.GitHubRepo, "https://")
+	add(panes.Field{Label: "issues", Value: github + "/issues", URL: update.GitHubRepo + "/issues"})
 	add(panes.Field{Label: "releases", Value: repo + "/releases", URL: update.DefaultRepo + "/releases"})
 	add(panes.Field{Label: "changelog", Value: repo + "/…/CHANGELOG.md", URL: update.DefaultRepo + "/src/branch/main/CHANGELOG.md"})
 	return append(out, m.changelog...)