Add EUR currency support for international transactions

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

backend/app/db.py

@@ -23,6 +23,12 @@ def run_migrations():
         except Exception:
             conn.rollback()
 
+        try:
+            conn.execute(text("ALTER TYPE currency ADD VALUE IF NOT EXISTS 'EUR'"))
+            conn.commit()
+        except Exception:
+            conn.rollback()
+
 
 def get_session():
     with Session(engine) as session: