Add endpoint for creating local contacts with access control

Introduced a new `local_contact_router` to handle creation of local contacts. The endpoint enforces role-based access control and ensures no duplication of email addresses. Updated the router exports for consistency and cleaned up a large test file to improve readability.

backend/app/database.py

@@ -77,6 +77,8 @@ def load_sample_data(session: Session):
         serial_numbers,
         slots,
         sample_events,
+        local_contacts,
+        beamtimes,
     )
 
     # If any data exists, don't reseed
@@ -95,5 +97,8 @@ def load_sample_data(session: Session):
         + serial_numbers
         + slots
         + sample_events
+        + local_contacts
+        + beamtimes
     )
+
     session.commit()