Fix OAuth server blocking: redirect subshell stdout (#30)

start_oauth_server was called inside $() to capture the PID, but the
backgrounded nc subshell inherited the $() stdout pipe. Since $()
waits for ALL writers to close, it blocked forever until nc exited
(which never happens — it's listening).

Fix: redirect the subshell's stdout/stderr to /dev/null so it doesn't
hold the pipe open. The PID echo still works because it runs in the
parent (after the & backgrounds the child).

Co-authored-by: Sprite <noreply@sprite.dev>
Co-authored-by: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

shared/common.sh

@@ -253,7 +253,7 @@ start_oauth_server() {
                     ;;
             esac
         done
-    ) </dev/null &
+    ) </dev/null >/dev/null 2>&1 &
 
     echo $!
 }