v0.7.9

feat: add auth auto-login and logout support

- Add "Remember password and auto login" option in Authentication dialog
- Persist username/password in localStorage (etcdkeeper_auth) when login succeeds
- Auto-connect on page load and reuse saved credentials if available
- Keep etcd endpoint / version / tree-mode / editor-mode stored in cookies
- Introduce ETCD_KEEPER_AUTH env var to control backend auth instead of hard-coded -auth flag
- Add Logout button in the top right to clear saved auth, reset UI, and reconnect unauthenticated