refactor(backend): standardize model-to-response conversion naming

Issue #8: Inconsistent naming for model-to-response conversion functions.

Changes:
- Rename build_invite_response to _to_invite_response (invites.py)
- Rename _map_counter_record to _to_counter_record_response (audit.py)
- Rename _map_sum_record to _to_sum_record_response (audit.py)

All conversion functions now follow the _to_X_response pattern,
using underscore prefix for module-private functions.

backend/routes/audit.py

@@ -61,7 +61,9 @@ async def paginate_with_user_email(
     return records, total, calculate_total_pages(total, per_page)
 
 
-def _map_counter_record(record: CounterRecord, email: str) -> CounterRecordResponse:
+def _to_counter_record_response(
+    record: CounterRecord, email: str
+) -> CounterRecordResponse:
     return CounterRecordResponse(
         id=record.id,
         user_email=email,
@@ -71,7 +73,7 @@ def _map_counter_record(record: CounterRecord, email: str) -> CounterRecordRespo
     )
 
 
-def _map_sum_record(record: SumRecord, email: str) -> SumRecordResponse:
+def _to_sum_record_response(record: SumRecord, email: str) -> SumRecordResponse:
     return SumRecordResponse(
         id=record.id,
         user_email=email,
@@ -91,7 +93,7 @@ async def get_counter_records(
 ) -> PaginatedCounterRecords:
     """Get paginated counter action records."""
     records, total, _ = await paginate_with_user_email(
-        db, CounterRecord, page, per_page, _map_counter_record
+        db, CounterRecord, page, per_page, _to_counter_record_response
     )
     return create_paginated_response(records, total, page, per_page)
 
@@ -105,7 +107,7 @@ async def get_sum_records(
 ) -> PaginatedSumRecords:
     """Get paginated sum action records."""
     records, total, _ = await paginate_with_user_email(
-        db, SumRecord, page, per_page, _map_sum_record
+        db, SumRecord, page, per_page, _to_sum_record_response
     )
     return create_paginated_response(records, total, page, per_page)
 

backend/routes/invites.py

@@ -31,7 +31,7 @@ admin_router = APIRouter(prefix="/api/admin", tags=["admin"])
 MAX_INVITE_COLLISION_RETRIES = 3
 
 
-def build_invite_response(invite: Invite) -> InviteResponse:
+def _to_invite_response(invite: Invite) -> InviteResponse:
     """Build an InviteResponse from an Invite with loaded relationships."""
     return InviteResponse(
         id=invite.id,
@@ -150,7 +150,7 @@ async def create_invite(
             status_code=status.HTTP_500_INTERNAL_SERVER_ERROR,
             detail="Failed to create invite",
         )
-    return build_invite_response(invite)
+    return _to_invite_response(invite)
 
 
 @admin_router.get("/invites", response_model=PaginatedInviteRecords)
@@ -197,7 +197,7 @@ async def list_all_invites(
     invites = result.scalars().all()
 
     # Build responses using preloaded relationships
-    records = [build_invite_response(invite) for invite in invites]
+    records = [_to_invite_response(invite) for invite in invites]
 
     return create_paginated_response(records, total, page, per_page)
 
@@ -230,7 +230,7 @@ async def revoke_invite(
     await db.commit()
     await db.refresh(invite)
 
-    return build_invite_response(invite)
+    return _to_invite_response(invite)
 
 
 # All routers from this module for easy registration