feat: add data_date to project summary response

Include the schedule data date (last_recalc_date from XER) in the
get_project_summary tool response. This shows when the schedule
was last calculated in P6.

Changes:
- Add last_recalc_date column to projects table schema
- Parse last_recalc_date in PROJECT table handler
- Include last_recalc_date in db loader
- Return data_date field in get_project_summary query
- Update contract test to verify data_date presence

tests/contract/test_get_project_summary.py

@@ -30,6 +30,7 @@ class TestGetProjectSummaryContract:
         result = await get_project_summary()
 
         assert "project_name" in result
+        assert "data_date" in result
         assert "plan_start_date" in result
         assert "plan_end_date" in result
         assert "activity_count" in result