fix(browser_tests): replace .nth() with semantic selectors

- Remove unused saveButton selector from ComfyMenu
- Replace widgetTextBox .nth(1) with node-scoped selector
- Replace .nth(3) toast selector with .p-toast-message filter
- Replace .nth(1) category selector with getByTestId
- Replace .nth(1) node selector with getNodeInFolder() helper
- Add nodeSelector(), folderSelector(), getNodeInFolder() methods
- Add saveButton and nodeLibrary TestIds to selectors.ts

Amp-Thread-ID: https://ampcode.com/threads/T-019c155c-92e1-76f3-b6ce-7fc3ffa11582
Co-authored-by: Amp <amp@ampcode.com>

browser_tests/fixtures/components/SidebarTab.ts

@@ -84,6 +84,20 @@ export class NodeLibrarySidebarTab extends SidebarTab {
       `[data-testid="node-tree-leaf"][data-node-name="${nodeName}"]`
     )
   }
+
+  nodeSelector(nodeName: string): string {
+    return `[data-testid="node-tree-leaf"][data-node-name="${nodeName}"]`
+  }
+
+  folderSelector(folderName: string): string {
+    return `[data-testid="node-tree-folder"][data-folder-name="${folderName}"]`
+  }
+
+  getNodeInFolder(nodeName: string, folderName: string) {
+    return this.getFolder(folderName)
+      .locator('xpath=ancestor::li')
+      .locator(`[data-testid="node-tree-leaf"][data-node-name="${nodeName}"]`)
+  }
 }
 
 export class WorkflowsSidebarTab extends SidebarTab {