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)

test/helpers/touchfiles.ts

@@ -80,9 +80,6 @@ export const E2E_TOUCHFILES: Record<string, string[]> = {
   'ship-base-branch': ['ship/**', 'bin/gstack-repo-mode'],
   'ship-local-workflow': ['ship/**', 'scripts/gen-skill-docs.ts'],
 
-  // Setup browser cookies
-  'setup-cookies-detect': ['setup-browser-cookies/**'],
-
   // Retro
   'retro':             ['retro/**'],
   'retro-base-branch': ['retro/**'],
@@ -207,9 +204,6 @@ export const E2E_TIERS: Record<string, 'gate' | 'periodic'> = {
   'ship-coverage-audit': 'gate',
   'ship-triage': 'gate',
 
-  // Setup browser cookies
-  'setup-cookies-detect': 'gate',
-
   // Retro — gate for cheap branch detection, periodic for full Opus retro
   'retro': 'periodic',
   'retro-base-branch': 'gate',