fix: Handle date conversion for string dates in data transformer

When resuming migration, EventDate may be a string (from PostgreSQL queries)
instead of a datetime.date object (from MySQL). The combine() function expects
a datetime.date object, so we now convert strings to dates before combining
with time.

Added _convert_date() helper similar to _convert_time() that handles:
- str: Parse from "YYYY-MM-DD" format
- datetime.date: Return as-is
- datetime.datetime: Extract date component

Fixes error: "combine() argument 1 must be datetime.date, not str"

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Haiku 4.5 <noreply@anthropic.com>

src/transformers/data_transformer.py

@@ -14,6 +14,30 @@ logger = get_logger(__name__)
 class DataTransformer:
     """Transform MySQL data to PostgreSQL format."""
 
+    @staticmethod
+    def _convert_date(event_date: Any) -> datetime.date:
+        """Convert event_date to datetime.date object.
+
+        Handles multiple input types:
+        - str: Parse from "YYYY-MM-DD" format
+        - datetime.date: Return as-is
+        - datetime.datetime: Extract date component
+
+        Args:
+            event_date: Date value from MySQL (str or date)
+
+        Returns:
+            datetime.date object
+        """
+        if isinstance(event_date, str):
+            return datetime.strptime(event_date, "%Y-%m-%d").date()
+        elif isinstance(event_date, datetime):
+            return event_date.date()
+        elif isinstance(event_date, datetime.date):
+            return event_date
+        else:
+            raise ValueError(f"Unsupported event_date type: {type(event_date)}")
+
     @staticmethod
     def _convert_time(event_time: Any) -> time:
         """Convert event_time to datetime.time object.
@@ -95,8 +119,9 @@ class DataTransformer:
         event_date = mysql_row.get("EventDate")
         event_time = mysql_row.get("EventTime")
         if event_date is not None and event_time is not None:
+            event_date_obj = DataTransformer._convert_date(event_date)
             event_time_obj = DataTransformer._convert_time(event_time)
-            event_timestamp = datetime.combine(event_date, event_time_obj)
+            event_timestamp = datetime.combine(event_date_obj, event_time_obj)
         elif event_date is None or event_time is None:
             # Log a warning for records with missing date/time
             missing = []
@@ -165,8 +190,9 @@ class DataTransformer:
         event_date = mysql_row.get("EventDate")
         event_time = mysql_row.get("EventTime")
         if event_date is not None and event_time is not None:
+            event_date_obj = DataTransformer._convert_date(event_date)
             event_time_obj = DataTransformer._convert_time(event_time)
-            event_timestamp = datetime.combine(event_date, event_time_obj)
+            event_timestamp = datetime.combine(event_date_obj, event_time_obj)
         elif event_date is None or event_time is None:
             # Log a warning for records with missing date/time
             missing = []