fix: browser test fixes for flaky selectors and missing setup

- SidebarTab: Use placeholder selector instead of test ID for search input
- KeyboardHelper: Remove redundant canvas fallback (null is valid)
- groupNode: Use variable for category name instead of hardcoded string
- nodeLibrary: Ensure tab is open before filling search input
- subgraph: Reload workflow after page reload to restore state
- useSettingSearch: Use role selector and simplify selected class assertion

Amp-Thread-ID: https://ampcode.com/threads/T-019c18c2-667a-7179-bb2d-86f35cd1d7b0
Co-authored-by: Amp <amp@ampcode.com>

browser_tests/tests/sidebar/nodeLibrary.spec.ts

@@ -385,6 +385,7 @@ test.describe('Node library sidebar', () => {
     ])
 
     const tab = comfyPage.menu.nodeLibraryTab
+    await tab.open()
     await tab.nodeLibrarySearchBoxInput.fill('KSampler')
     await expect(tab.getNode('KSampler (Advanced)')).toHaveCount(2)
   })