Replaced login, reset password modal, and sign-up screenshots in the gallery. Updated gallery.md to specify that images should be 1000x1000 pixels. Also updated the login asset in the frontend.
Added new screenshots for health, settings, and authentication pages, updated several existing images, and removed obsolete ones. The gallery documentation was updated to reflect the new and reorganized screenshots, providing a more comprehensive and up-to-date visual overview of the application's UI. Minor formatting cleanups were also made in the developer and getting started guides.
