feat: add web frontend directory structure

- Create web/src/ for TypeScript source files
- Create web/static/ for compiled assets and runtime files
- Move input.css and style.css to web/static/
- Add toast.ts - Functional toast notification system
- Add theme.ts - Functional theme management system
- All code uses functional programming (no classes, no OOP)
- TypeScript provides full type safety

Separates frontend code from backend for better organization.

web/static/input.css

@@ -0,0 +1,5 @@
+@tailwind base;
+@tailwind components;
+@tailwind utilities;
+
+/* Custom theme variables are handled in CSS custom properties in templates */