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

src/xer_mcp/parser/table_handlers/project.py

@@ -35,4 +35,5 @@ class ProjectHandler(TableHandler):
             "proj_short_name": data.get("proj_short_name", ""),
             "plan_start_date": convert_date(data.get("plan_start_date")),
             "plan_end_date": convert_date(data.get("plan_end_date")),
+            "last_recalc_date": convert_date(data.get("last_recalc_date")),
         }