[WIP] Add project introduction webpage layout

[Copilot]

• Analyze existing code structure and routing
• Create an introduction page template with project information
• Add a new route handler for the introduction page (e.g., /about or /intro)
• Add navigation between the introduction page and the main request viewer
• Support both English and Chinese languages (matching existing i18n pattern)
• Test the introduction page locally
• Verify no existing functionality is broken

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