Browser agent gym

Test pages with no student data. gym.json lists each scenario and what the press should mean.

• blob-b64 -> pdf
• blob-json -> pdf
• fetch-only -> pdf
• raw-link -> pdf
• gzip -> pdf
• expired -> not-a-document
• empty-download -> pdf
• in-iframe -> pdf
• faq-pay -> reveal
• complete-tab -> navigate
• payment-info-link -> navigate
• pay-now-link -> payment
• save-section -> send
• confirm-send -> final
• weiter-zahlung -> payment
• icon-only-submit -> final
• ok-in-payment-modal -> payment
• finish-wizard -> final
• submit-docs-toggle -> reveal