fix: Uncheck action is never generated in browser test scripts

CheckExpression.checked was typed as Expression (an IR AST node object)
but used in a boolean context to decide between 'check' and 'uncheck'
method names. Since an object is always truthy, the uncheck branch was
unreachable and locator.uncheck() was never emitted in generated scripts.

Change CheckExpression.checked from Expression to boolean so the
ternary in emitCheckExpression works correctly. Update the intermediate
emitter to pass the boolean directly and fix the variable substitution
pass to preserve the boolean instead of calling substituteExpression.

The test snapshot for uncheck-element was also wrong (showed .check()
instead of .uncheck()), confirming the bug existed since the snapshot
was first captured.

Co-authored-by: Edgar Fisher <e-fisher@users.noreply.github.com>

Author: cursoragent

src/codegen/browser/__snapshots__/browser/uncheck-element.ts

@@ -15,7 +15,7 @@ export default async function () {
   const page = await browser.newPage();
 
   try {
-    await page.locator('input[type="checkbox"]').check();
+    await page.locator('input[type="checkbox"]').uncheck();
   } finally {
     await page?.close();
   }

src/codegen/browser/intermediate/ast.ts

@@ -96,7 +96,7 @@ export interface ClickExpression {
 export interface CheckExpression {
   type: 'CheckExpression'
   locator: Expression
-  checked: Expression
+  checked: boolean
 }
 
 export interface SelectOptionsExpression {

src/codegen/browser/intermediate/index.ts

@@ -243,10 +243,7 @@ function emitCheckNode(context: IntermediateContext, node: m.CheckNode) {
     expression: {
       type: 'CheckExpression',
       locator,
-      checked: {
-        type: 'StringLiteral',
-        value: node.checked ? 'checked' : 'unchecked',
-      },
+      checked: node.checked,
     },
   })
 }

src/codegen/browser/intermediate/variables.ts

@@ -149,7 +149,7 @@ function substituteExpression(
     case 'CheckExpression':
       return {
         type: 'CheckExpression',
-        checked: substituteExpression(node.checked, substitutions),
+        checked: node.checked,
         locator: substituteExpression(node.locator, substitutions),
       }