fix: remove unsupported theme parameter tab_selected_text_color

Gradio 6.0 doesn't support this parameter in Base.set()

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

src/ui/theme.py

@@ -95,8 +95,6 @@ class UpscalerTheme(Base):
             table_border_color="*neutral_700",
             table_even_background_fill="*neutral_850",
             table_odd_background_fill="*neutral_900",
-            # Tabs
-            tab_selected_text_color="*primary_400",
         )