fix(lit): use .checked instead of .value in checkbox component

The checkbox component incorrectly used .value (string) instead of
.checked (boolean) for both display binding and event handling:

- Changed .value=\ to .checked=\ for property binding
- Changed evt.target.value to evt.target.checked in event handler
- Updated #setBoundValue signature from string to boolean

This aligns the Lit implementation with the Angular reference
implementation and the A2UI protocol specification which states
checkbox value should be 'true for checked, false for unchecked'.

Author: shantoislamdev

renderers/lit/src/0.8/ui/checkbox.ts

@@ -57,7 +57,7 @@ export class Checkbox extends Root {
     `,
   ];
 
-  #setBoundValue(value: string) {
+  #setBoundValue(value: boolean) {
     if (!this.value || !this.processor) {
       return;
     }
@@ -93,11 +93,11 @@ export class Checkbox extends Root {
             return;
           }
 
-          this.#setBoundValue(evt.target.value);
+          this.#setBoundValue(evt.target.checked);
         }}
         id="data"
         type="checkbox"
-        .value=${value}
+        .checked=${value}
       />
       <label class=${classMap(this.theme.components.CheckBox.label)} for="data"
         >${this.label?.literalString}</label