chore: remove operator seed script + gitignore local verification artifacts

- git rm apps/api/scripts/seed-credential.mjs (operator-only, run out-of-band;
  the credential is already seeded in the running DB)
- gitignore .playwright-cli/, gate2-*.png, and the seed script path

.gitignore

@@ -35,3 +35,10 @@ pnpm-debug.log*
 # Test coverage
 coverage/
 .nyc_output/
+
+# Playwright CLI artifacts + ad-hoc screenshots (local verification only)
+.playwright-cli/
+gate2-*.png
+
+# Operator-only credential seed (run out-of-band; never tracked)
+apps/api/scripts/seed-credential.mjs