fix: require Gradio 6.0+ for css in launch() API

Gradio 6.0 moved css parameter from Blocks() to launch().
This aligns the dependency with README.md sdk_version and
resolves CodeRabbit's warning about API compatibility.

pyproject.toml

@@ -17,7 +17,7 @@ dependencies = [
     "beautifulsoup4>=4.12", # HTML parsing
     "xmltodict>=0.13", # PubMed XML -> dict
     # UI
-    "gradio[mcp]>=5.32.0", # Chat interface with MCP server support
+    "gradio[mcp]>=6.0.0", # Chat interface with MCP server support (6.0 required for css in launch())
     # Utils
     "python-dotenv>=1.0", # .env loading
     "tenacity>=8.2", # Retry logic

requirements.txt

@@ -13,7 +13,7 @@ beautifulsoup4>=4.12
 xmltodict>=0.13
 
 # UI (Gradio with MCP server support)
-gradio[mcp]>=5.32.0
+gradio[mcp]>=6.0.0
 
 # Utils
 python-dotenv>=1.0