Ignore Gradio's auto-generated app.pyi stub

Gradio writes a type-stub .pyi next to the entrypoint when the Blocks
is loaded, which kept dirtying the working tree after every local
run.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

.gitignore

@@ -6,6 +6,9 @@ dist/
 wheels/
 *.egg-info
 
+# Gradio writes an app.pyi stub alongside the entrypoint on Blocks load
+app.pyi
+
 # Virtual environments
 .venv