fix(lit): use .checked instead of .value in checkbox component [Issue #458]

[shantoislamdev]

Summary

Fix checkbox component to use .checked property instead of .value for correct boolean state binding.

Problem

The Lit checkbox incorrectly uses .value and evt.target.value:

Current (Bug)	Expected
.value=${value}	.checked=${value}
evt.target.value	evt.target.checked
Returns string	Returns boolean

Impact:

• Checkbox doesn't display checked state visually
• Event handler reads wrong property (always returns same string)
• Data model receives string instead of boolean, corrupting state

Solution

Changed three lines in [renderers/lit/src/0.8/ui/checkbox.ts]

1. Line 60: Updated method signature from string to boolean
2. Line 96: Changed evt.target.value → evt.target.checked
3. Line 100: Changed .value=${value} → .checked=${value}

Evidence

The Angular checkbox implementation correctly uses:

• [checked]="inputChecked()" (line 32)
• event.target.checked (line 71)

See: [renderers/angular/src/lib/catalog/checkbox.ts]

Testing

• npm install ✅
• TypeScript build (npx tsc -b) ✅
• Tests pass: 23/23 ✅

Checklist

• I have signed the Google CLA
• My code follows the project's style guidelines
• I have tested my changes locally

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