Refactor: Checkbox uses U+25FC (black small square)

- Changed indicator from ◾ to ◼ (U+25FC)
- Smaller, more compact checkbox appearance
- Updated example page state summary
- All 571 tests passing

Sources/TUIkit/Views/Toggle.swift

@@ -141,8 +141,8 @@ extension Toggle: Renderable {
         case .toggle:
             indicatorContent = isOn.wrappedValue ? "●○" : "○●"
         case .checkbox:
-            // U+25FE: Black medium square
-            indicatorContent = isOn.wrappedValue ? "\u{25FE}" : " "
+            // U+25FC: Black small square
+            indicatorContent = isOn.wrappedValue ? "\u{25FC}" : " "
         }
 
         // Determine bracket color: pulsing accent when focused, border when unfocused

Sources/TUIkitExample/Pages/TogglePage.swift

@@ -59,11 +59,11 @@ struct TogglePage: View {
                     }
                     HStack(spacing: 1) {
                         Text("Hidden Files:").foregroundColor(.palette.foregroundSecondary)
-                        Text(advancedOptionsEnabled ? "[\u{25FE}]" : "[ ]").foregroundColor(.palette.accent)
+                        Text(advancedOptionsEnabled ? "[\u{25FC}]" : "[ ]").foregroundColor(.palette.accent)
                     }
                     HStack(spacing: 1) {
                         Text("Analytics:").foregroundColor(.palette.foregroundSecondary)
-                        Text(analitycsEnabled ? "[\u{25FE}]" : "[ ]").foregroundColor(.palette.accent)
+                        Text(analitycsEnabled ? "[\u{25FC}]" : "[ ]").foregroundColor(.palette.accent)
                     }
                 }
             }