fix: address PR #574 second review round

- Enrich single-calendar event dicts with calendar_name before mapping
  to CalendarEventSummary (list_events and upcoming_events paths)
- Extract _raw_contact_to_model() from inline mapping in contacts.py,
  fix custom_fields type annotation to dict[str, Any]
- Add unit tests for _event_dict_to_summary covering categories parsing,
  falsy coercion, and calendar name passthrough
- Replace duplicated test helper with import of production function

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

nextcloud_mcp_server/server/calendar.py

@@ -240,6 +240,10 @@ def configure_calendar_tools(mcp: FastMCP):
                 limit=limit,
             )
 
+            # Enrich events with calendar context for per-event mapping
+            for event in events:
+                event["calendar_name"] = calendar_name
+
             # Apply filters if provided
             if filters:
                 events = client.calendar._apply_event_filters(events, filters)
@@ -459,6 +463,8 @@ def configure_calendar_tools(mcp: FastMCP):
                 end_datetime=end_datetime,
                 limit=limit,
             )
+            for event in events:
+                event["calendar_name"] = calendar_name
         else:
             # Get events from all calendars
             all_calendars = await client.calendar.list_calendars()