docs: sync project documentation

[RANDAAAALL]

Description

• Replace default Vite frontend README with complete setup and architecture guide
• Add 'Current Implementation Snapshot' to root README
• Update ARCHITECTURE.md to distinguish implemented vs planned features
• Clean up directory structure documentation and add testing folders

Type of Change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation update
• Code refactoring
• Performance improvement
• Other (please describe):

Testing

• Build passes (npm run build for frontend, pytest for backend)
• Type check passes (npm run typecheck for frontend)
• Tested locally
• All existing tests pass

Related Issues

• Related to [Docs]: Sync project documentation with current implementation #41

Checklist

• Code follows project conventions (see ARCHITECTURE.md)
• No any types used unnecessarily (TypeScript)
• Proper error handling implemented
• Loading states added (if applicable)
• Responsive design tested (if UI changes)
• Self-review completed
• Comments added for complex logic
• Documentation updated (if needed)

Breaking Changes

None

Deployment Notes

None

Additional Context

This PR officially closes out the foundational backlog, bringing the documentation up to speed with the newly integrated data-driven pages, chat engine, and auth flows.

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Review Notes:

Reviewer: Please indicate whether to squash commits or preserve history when merging.