Release 2.7.3.1: harden proxy recovery, updates and local API.

Restore orphaned system proxy after crash, require update SHA-256, add macOS /api auth token, fix UDP ping false positives, HTTPS-only subscriptions, and keep the UI responsive during connect.

Co-authored-by: Cursor <cursoragent@cursor.com>

internal/netcheck/ping.go

@@ -212,7 +212,8 @@ func probeUDP(ctx context.Context, host, port string) error {
 		return nil
 	}
 	if ne, ok := err.(net.Error); ok && ne.Timeout() {
-		return nil
+		// UDP is connectionless: no reply does NOT mean the port is open.
+		return fmt.Errorf("udp timeout")
 	}
 	return err
 }