feat: port retail magic lifecycle and retained spell UI

Complete the retail cast-intent, target, component, enchantment, and busy-state paths; mount the DAT-authored spell bar, spellbook, component book, effects panels, and shared panel lifecycle; and add scoped input plus conformance coverage.

Co-Authored-By: Codex <noreply@openai.com>

src/AcDream.App/UI/UiField.cs

@@ -61,6 +61,7 @@ public sealed class UiField : UiElement
     private int _caret;
     private int? _selAnchor;   // selection fixed end (null = no selection); span = [min,max] with _caret
     public string Text => _text;
+    public bool IsFocused => _focused;
     public int CaretPos => _caret;
 
     private readonly List<string> _history = new();