Pin Space to gradio 6.19.0 to fix startup crash

gradio 5.9.1's API-info generator (gradio_client json_schema_to_python_type)
crashes on gr.JSON component schemas with "TypeError: argument of type
'bool' is not iterable", which fails the Space's startup health check
("localhost is not accessible") and exits the container. The app was
developed and browser-verified against gradio 6.19.0, where this is
fixed, so pin sdk_version (and the local dev floor) to match.

README.md

@@ -4,7 +4,7 @@ emoji: 📄
 colorFrom: blue
 colorTo: gray
 sdk: gradio
-sdk_version: 5.9.1
+sdk_version: 6.19.0
 app_file: app.py
 pinned: false
 license: mit

requirements.txt

@@ -1,4 +1,4 @@
-gradio>=5.0.0
+gradio>=6.0.0
 pymupdf>=1.24.0
 pytesseract>=0.3.10
 pillow>=10.0.0