Merge branch 'feat/studies' into 'dev'

backend/alembic/versions/0bf670c4a564_study_users.py

backend/app/crud.py

backend/app/main.py

backend/app/models.py

backend/app/schemas.py

frontend/package-lock.json

frontend/src/lang/en.json

frontend/src/lang/fr.json

frontend/src/lib/api/studies.ts

frontend/src/lib/api/users.ts

frontend/src/lib/components/utils/dateInput.svelte

frontend/src/lib/types/study.ts

frontend/src/lib/utils/date.ts

frontend/src/routes/Header.svelte

frontend/src/routes/admin/studies/+page.svelte

frontend/src/routes/admin/studies/+page.ts

frontend/src/routes/admin/users/+page.svelte

frontend/src/routes/admin/users/+page.ts

frontend/src/routes/register/[[studyId]]/+page.server.ts

frontend/src/routes/register/[[studyId]]/+page.svelte