fix: add @bgotink/playwright-coverage to knip ignoreDependencies

The knip playwright plugin does not detect the import from
playwright.config.ts, causing a false unused-dependency error.

Addresses review feedback:
https://github.com/Comfy-Org/ComfyUI_frontend/pull/10930#discussion_r3047998511

knip.config.ts

@@ -48,7 +48,9 @@ const config: KnipConfig = {
     '@primeuix/forms',
     '@primeuix/styled',
     '@primeuix/utils',
-    '@primevue/icons'
+    '@primevue/icons',
+    // Used in playwright.config.ts for coverage collection
+    '@bgotink/playwright-coverage'
   ],
   ignore: [
     // Auto generated API types