fix: remove theme parameter for Gradio 6.0 compatibility

Gradio 6.0.1 doesn't support the theme parameter in gr.Blocks().
The dark styling is now provided entirely through the custom CSS.

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

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

src/ui/app.py

@@ -5,7 +5,7 @@ import torch
 import gradio as gr
 
 from src.config import config
-from src.ui.theme import get_theme, get_css
+from src.ui.theme import get_css
 from src.ui.components.image_tab import create_image_tab
 from src.ui.components.video_tab import create_video_tab
 from src.ui.components.batch_tab import create_batch_tab
@@ -30,14 +30,12 @@ def get_gpu_status() -> str:
 
 def create_app() -> gr.Blocks:
     """Create and return the main Gradio application."""
-    theme = get_theme()
     css = get_css()
 
+    # Gradio 6.0+ compatible Blocks initialization
     with gr.Blocks(
-        theme=theme,
         css=css,
         title="Real-ESRGAN Upscaler",
-        fill_width=True,
     ) as app:
         # Header
         gr.HTML(