feat: ai samples impl text gen/chat

[sedanah-m]

Implement text-generation and chat samples. Add decoupled logic so that user can run script to start either sample.

[gemini-code-assist]

Code Review

This pull request introduces a modular React and Vite-based application showcasing Firebase AI capabilities, including text generation and multi-turn chat. Feedback on the changes highlights several critical issues: an invalid model name ('gemini-3.5-flash') is used across multiple service files, which will cause runtime failures; the Chat view lacks error handling during initialization, potentially leading to application crashes; Firebase configuration values are hardcoded instead of using environment variables; and a deprecated @types/react-router-dom dependency is present, risking type conflicts with React Router v7.

[gemini-code-assist]

If Firebase is not configured or fails to initialize, startNewChat() will throw an unhandled exception on mount inside useEffect, causing the entire React application to crash with a white screen. Wrapping this initialization in a try/catch block and setting the error state allows the UI to gracefully display the error.

  const handleResetChat = () => {
    try {
      chatSessionRef.current = startNewChat();
      setError(null);
    } catch (err: any) {
      setError(err.message || 'Failed to initialize chat session. Please check your Firebase configuration.');
    }
    setMessages([]);
    setInput('');
  };