feat(element/button): add builtin Element implementation for buttons

examples/elements/button.zig

@@ -89,6 +89,8 @@ pub fn main() !void {
     var clickable: Clickable = .{ .queue = &app.queue };
     const element = clickable.element();
 
+    var button: App.Button(.accept) = .init(&app.queue, .init(.default, "Button"));
+
     var quit_text: QuitText = .{};
 
     var container = try App.Container.init(allocator, .{
@@ -98,6 +100,7 @@ pub fn main() !void {
     defer container.deinit();
 
     try container.append(try App.Container.init(allocator, .{ .rectangle = .{ .fill = .light_grey } }, element));
+    try container.append(try App.Container.init(allocator, .{ .rectangle = .{ .fill = .black } }, button.element()));
 
     try app.start();
     defer app.stop() catch |err| log.err("Failed to stop application: {any}", .{err});
@@ -110,9 +113,8 @@ pub fn main() !void {
         // pre event handling
         switch (event) {
             .key => |key| if (key.eql(.{ .cp = 'c', .mod = .{ .ctrl = true } })) app.quit(),
-            .click => |button| {
-                log.info("Clicked with mouse using Button: {s}", .{button});
-            },
+            .click => |b| log.info("Clicked with mouse using Button: {s}", .{b}),
+            .accept => log.info("Clicked built-in button using the mouse", .{}),
             .err => |err| log.err("Received {s} with message: {s}", .{ @errorName(err.err), err.msg }),
             else => {},
         }
@@ -145,4 +147,5 @@ const assert = std.debug.assert;
 const zterm = @import("zterm");
 const App = zterm.App(union(enum) {
     click: [:0]const u8,
+    accept,
 });