chore(examples): add qa_ping smoke workflow; ignore tui-go binary and qa/ scratch

qa_ping is a minimal single-stage file_write workflow used for live QA smoke
runs (writes 'pong' into the qa/ scratch repo). The qa/ workspace itself is a
nested git repo and stays untracked; the compiled tui-go binary is ignored.

.gitignore

@@ -81,3 +81,6 @@ apps/tui/logs/
 
 # Server runtime logs
 apps/server/logs/
+
+# local QA scratch workspace (nested git repo)
+/qa/