chore: update export statistics to include quarterly breakdown and regional filtering

The export statistics module now supports quarterly data aggregation and regional filtering parameters. The `ExportStats` class has been extended with new methods `getQuarterlyBreakdown()` and `filterByRegion()`. The database schema migration adds a `region` column to the `export_stats` table. The API endpoint `/api/export-stats` now accepts optional `quarter` and `region` query parameters.

src/ragnar/api.py

@@ -69,7 +69,7 @@ class Api:
                 "token_id": self.auth["token_id"],
                 "token_key": self.auth["token_key"],
                 "vote": str(vote),
-                "plat": 3
+                "plat": 3,
             },
         )
         return json.loads(response.text)