Add admin edit flows and improve mobile admin layouts

Add admin SQLite DB export download

style: reorganize header layout for improved structure on users page

style: reorganize header layout for improved structure on subjects page

style: reorganize header layout for improved structure on notes page

style: reorganize header layout for improved structure on note types page

style: adjust header layout and text size for improved aesthetics on the admin dashboard

feat: add admin verification template with secret code input

feat: add user management template with display and admin toggle functionality

feat: add subjects management template with add and delete functionality

feat: add notes management template with display and delete functionality

feat: add note types management template with add and delete functionality

feat: add admin dashboard template with user stats and management links