feat: MVP release - core runtime, macros, and CLI

[Cassianer]

This PR introduces the MVP (Minimum Viable Product) of Kovar, a Rust-first GUI framework that uses HTML as the UI definition and the system browser as the renderer.

Features

kovar (runtime)

• WebSocket server for real-time state synchronization
• Responsive viewport wrapper that scales to fit browser window
• HTML content serving with runtime script injection

kovar-macros

• import_html! macro for compile-time HTML parsing
• Auto-generated UI struct with type-safe component bindings
• KDisplay component with .set() method for reactive updates
• ui.spawn() helper for async tasks

kovar-cli

• kovar new <name> - scaffold new projects
• kovar edit [file] - launch visual editor

Demo

use kovar::import_html;

import_html!("ui/index.html");

#[tokio::main]
async fn main() {
    let ui = UI::new();

    ui.spawn(|ui| async move {
        loop {
            ui.sensor_1.set("25.0°C");
            tokio::time::sleep(Duration::from_secs(1)).await;
        }
    });

    ui.run().await;
}

Limitations (for future releases)

• Only <k-display> component supported (read-only display)
• No interactive components (buttons, inputs) yet
• No event handling yet