feat: add suggested prompts on empty chat

[Yuva-Deekshitha-N]

Resolves #126

Description

• Display suggested prompts when the chat is empty
• Clicking a prompt inserts it into the input box
• Prompts hide after the first message is sent
• Prompts reappear after clearing the chat

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Related Issue

Fixes #126

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Type of Change

• Bug fix
• New feature
• Enhancement
• Documentation update
• Refactoring
• Performance improvement
• Tests
• Other (please specify)

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Changes Made

• Added hasStarted state to track if conversation has begun
• Added SUGGESTED_PROMPTS array with 4 example questions
• Rendered prompt chips above response area, hidden after first query
• Added styles for .suggested-prompts and .prompt-chip in App.css

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Testing

• Tested locally
• Existing tests pass
• Added new tests (if applicable)

Additional Notes:

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Screenshots (if applicable)

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Checklist

• My code follows the project's coding style.
• I have linked the related issue.
• I have tested my changes.
• I have updated documentation where necessary.
• My changes do not introduce new warnings or errors.
• The project builds successfully.
• This PR only addresses the linked issue.