refactor: update Gradio UI theme and custom CSS to light Google Gemini style

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refactor: wrap ChatInterface in gr.Blocks to support custom theme and CSS

refactor: replace custom HTML head with native title and description in ChatInterface

feat: replace sentiment analysis demo with Gemma 4 chat assistant application

Support ZeroGPU with @spaces.GPU decorator

Add requirements and Sentiment Analysis app

Add application file

initial commit