fix(falukant): validate office term length and adjust term end calculation

- Added validation for office term length to ensure it is a positive finite number, throwing an error for invalid values.
- Updated the calculation of the term end date to use the term length in days instead of years, aligning with the expected data format.

backend/services/falukantPoliticalPowersService.js

@@ -457,8 +457,14 @@ class FalukantPoliticalPowersService {
         }
 
         const start = new Date();
+        const termDays = Number(officeType.termLength);
+        if (!Number.isFinite(termDays) || termDays <= 0) {
+            const err = new Error('invalid_office_term_length');
+            err.status = 500;
+            throw err;
+        }
         const end = new Date(start);
-        end.setFullYear(end.getFullYear() + (officeType.termLength || 4));
+        end.setDate(end.getDate() + termDays);
 
         let newOffice;
         await sequelize.transaction(async (t) => {