chore: gitignore stray tester.yaml test account

Prevents git add -A from sweeping a local browser-test account (with its
password hash) into the content repo, matching the existing testrunner.yaml
ignore.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01H1FrCYNq6RXdGYbn5PFrhM

.gitignore

@@ -5,6 +5,7 @@
 !/plugins/entry-actions/
 /data/
 /accounts/testrunner.yaml
+/accounts/tester.yaml
 /pages/01.trips/italy-2026-demo/
 /pages/02.post/*ui-test*/
 /config/plugins/git-sync.yaml