feat(engine): add layout, LayoutResource, and TablePlugin

compute_layout is a pure function that maps window size to card size and
the 13 pile positions, with clamping at the 800x600 minimum and seven
tableau columns horizontally aligned with stock/waste (cols 0,1) and the
four foundations (cols 3,4,5,6). TablePlugin spawns a 2D camera, a felt
background sprite, and 13 translucent pile-marker sprites, and
repositions them on WindowResized. Plugin registers WindowResized
explicitly so it works under MinimalPlugins in tests.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

solitaire_app/src/main.rs

@@ -1,5 +1,5 @@
 use bevy::prelude::*;
-use solitaire_engine::GamePlugin;
+use solitaire_engine::{GamePlugin, TablePlugin};
 
 fn main() {
     App::new()
@@ -14,5 +14,6 @@ fn main() {
             }),
         )
         .add_plugins(GamePlugin)
+        .add_plugins(TablePlugin)
         .run();
 }