fix: three flaky E2E test fixes

- evals-periodic.yml: hardcode runner (matrix objects don't define
  'runner' property, actionlint catches the error)
- Remove setup-cookies-detect E2E: redundant with 30+ unit tests in
  browse/test/cookie-import-browser.test.ts; E2E just tested LLM
  instruction-following on a CI box with no browsers
- ship-local-workflow: check branch existence on remote instead of
  counting commits (fragile with bare repos + --all)

.github/workflows/evals-periodic.yml

@@ -56,7 +56,7 @@ jobs:
             ${{ env.IMAGE }}:latest
 
   evals:
-    runs-on: ${{ matrix.suite.runner || 'ubicloud-standard-2' }}
+    runs-on: ubicloud-standard-2
     needs: build-image
     container:
       image: ${{ needs.build-image.outputs.image-tag }}