Exit non-zero when any errors are logged during bootstrap run

Track error count in issues.go alongside the existing issues slice.
Add hasErrors() helper. In main.go, call osExit(1) after writeRunLog()
if any [ERROR] entries were recorded, so CI steps correctly fail when
errors occur (e.g. GitHub API 403 rate-limit hits in the macOS job).

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

issues.go

@@ -13,9 +13,10 @@ import (
 // when there's something to report.
 
 var (
-	issuesMu sync.Mutex
-	issues   []string
-	notices  []string
+	issuesMu   sync.Mutex
+	issues     []string
+	notices    []string
+	errorCount int
 )
 
 func logIssue(level, msg string) {
@@ -23,11 +24,20 @@ func logIssue(level, msg string) {
 	defer issuesMu.Unlock()
 	fmt.Printf("  [%s] %s\n", level, msg)
 	issues = append(issues, fmt.Sprintf("[%s] %s", level, msg))
+	if level == "ERROR" {
+		errorCount++
+	}
 }
 
 func warn(msg string)   { logIssue("WARN", msg) }
 func errLog(msg string) { logIssue("ERROR", msg) }
 
+func hasErrors() bool {
+	issuesMu.Lock()
+	defer issuesMu.Unlock()
+	return errorCount > 0
+}
+
 func notice(msg string) {
 	issuesMu.Lock()
 	defer issuesMu.Unlock()