Implement comprehensive theme system with calendar view support

- Add 8 attractive themes (Default, Ocean, Forest, Sunset, Purple, Dark, Rose, Mint)
- Extend theme system to calendar header, month view, and week view components
- Add dynamic theme-aware event color palettes that change with selected theme
- Implement CSS custom properties for consistent theming across all components
- Add localStorage persistence for user theme preferences
- Create theme-aware calendar styling including day states, headers, and grid lines
- Optimize dark theme with proper contrast and readability improvements
- Add reactive event color system that updates when themes change

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

Cargo.toml

@@ -24,6 +24,7 @@ web-sys = { version = "0.3", features = [
     "RequestInit",
     "RequestMode",
     "Response",
+    "CssStyleDeclaration",
 ] }
 wasm-bindgen = "0.2"