e2e: pin Playwright to 1.59.1

`@playwright/test` was loose-pinned to ^1.50.0; npm resolved it
to 1.59.1 inside the runner image, which only ships browser
binaries for 1.50.0. Pin both the package and the docker image
to v1.59.1 so deps and binaries stay aligned.

e2e/playwright/package.json

@@ -9,6 +9,6 @@
     "test:debug": "PWDEBUG=1 playwright test"
   },
   "devDependencies": {
-    "@playwright/test": "^1.50.0"
+    "@playwright/test": "1.59.1"
   }
 }