Add optional-parameter overloads for common layout and text widgets #9

Context

A dashboard is mostly layout, and the struct-initializer API makes every container two or three lines. My 50-line header is almost entirely new Box { ... }:

using (ui.Row(new Box { Align = Align.Center, Gap = 12 }))
using (ui.Column(new Box { Pad = 18, Gap = 12, Height = Size.Fill }))

Proposal

Optional-parameter overloads for the hot fields, keeping the struct API for the long tail:

ui.Row(gap: 12, align: Align.Center)
ui.Column(pad: 18, gap: 12, height: Size.Fill)
ui.Text("Live", size: 12, color: Color.TextSecondary)
ui.Badge("Updating", Tone.Danger)
ui.Card(pad: 16, gap: 12, dir: Dir.Column)

Same treatment for the Size/Variant/Width trio on Segmented and Button.

Why

It is an authoring cost, but it also makes skill/docs examples shorter and harder to get wrong — the current snippets carry enough braces that a missing using is easy to miss (which is exactly what CUI002 then has to catch).