fix: targeted extract not allowing xpath= (#887)

# why
- we were passing the wrong variable to `getAccessibilityTree` which
broke targeted extract for selectors with the `xpath=` prefix
# what changed
- pass the parsed xpath instead of the raw selector
# test plan
- targeted extract evals

Author: seanmcguire12

.changeset/hot-geckos-build.md

@@ -0,0 +1,5 @@
+---
+"@browserbasehq/stagehand": patch
+---
+
+fix: allow xpaths with prepended 'xpath=' for targeted extract

lib/handlers/extractHandler.ts

@@ -156,7 +156,7 @@ export class StagehandExtractHandler {
           combinedXpathMap: {} as Record<EncodedId, string>,
           discoveredIframes: [] as undefined,
         }))
-      : getAccessibilityTree(this.stagehandPage, this.logger, selector).then(
+      : getAccessibilityTree(this.stagehandPage, this.logger, targetXpath).then(
           ({ simplified, idToUrl, iframes: frameNodes }) => ({
             combinedTree: simplified,
             combinedUrlMap: idToUrl as Record<EncodedId, string>,