feat: integrate surf-display UI framework into surf-api

[Copilot]

Ports the surf-display map-based Display/UI framework into surf-api, following the existing API/impl module split.

API module (dev.slne.surf.api.paper.display)

• Element tree: Element, Div, Label, ImageElement, ShapeElement — DOM-like hierarchy with Kotlin DSL builders
• Style system: CSS-like Style class — flex layout, padding/margin/border, text alignment, overflow, cursor style
• Shape primitives: Circle, Rectangle, Ellipse, Triangle, Line, RoundedRectangle, Polygon via Shape interface with BitSet rasterization
• Behavior system: Clickable, Hoverable, Draggable, Scrollable, TooltipBehavior — composable interaction handlers
• Renderer: Two-phase layout (border-box flexbox) + paint onto Canvas pixel buffer
• Document DSL: document(width, height) { ... } entry point

Server module (dev.slne.surf.api.paper.server.display)

• Display: Spawns invisible item frame wall, renders Canvas tiles to map packets, software cursor overlay
• DisplaySession: Fake player camera + invisible horse mount for yaw/pitch → pixel cursor mapping
• DisplayProtocolListener: PacketEvents listener wiring rotation/click/sneak packets to display interactions
• DisplayLoader: Registered in PaperInstance for lifecycle management
• Modal system: confirmDialog(), alertDialog(), successDialog(), errorDialog(), warningDialog()
• Web support: WebDisplay/WebRenderer/JavaFxPlatform for HTML rendering via offscreen JavaFX WebView

Test plugin

• /surfapitest display open|close — demo with shapes, hover buttons, modal dialog, text alignment

Example usage

val doc = document(384, 256) {
    style { backgroundColor = color(0x1E1E2E); padding = Insets.all(8); gap = 6 }
    div {
        label("Hello Display") { style { color = color(0xCDD6F4); fontSize = 16 } }
        div {
            style { cursor = CursorStyle.POINTER; border = Border(1, color(0xA6E3A1)) }
            label("Click me") { style { color = color(0xA6E3A1) } }
            hoverable(
                onEnter = { style.backgroundColor = color(0x45475A); display.update() },
                onExit  = { style.backgroundColor = null; display.update() }
            )
            onClick { ctx -> player.sendMessage("Clicked at ${ctx.pixelX},${ctx.pixelY}") }
        }
    }
}
DisplayManager.open(player, Display(doc))

[TheBjoRedCraft]

Keine Ahnung ob man das irgendwann mal reinpacken möchte
, braucht denke ich noch viele Verbesserungen.