Refactor and Organize Knitlab Codebase

[areumjo]

1. Decouple State from App.tsx

Issue: App.tsx acts as a "God Component".
Solution: Introduce Context APIs for keyPalette and sheets. Refactor consuming components accordingly.

2. Extract Logic into Custom Hooks

Issue: Large components (e.g., KnitCanvas.tsx, KeyEditorModal.tsx) are too complex.
Solution: Move interaction, drawing, and editing logic into dedicated hooks (useCanvasInteraction, useCanvasDrawing, useLineDrawer).

3. Organize Project Structure

Issue: Flat structure with mixed responsibilities.
Solution: Group components by feature and move utilities (e.g., grid helpers) to services or utils.

Summary: These changes will make the codebase cleaner, more maintainable, and ready for future growth. Let us know for review or PR collaboration.