Fix TypeScript errors in financial validation

backend/src/services/simpleDocumentProcessor.ts

@@ -536,9 +536,9 @@ Focus on finding these specific fields in the document. Extract exact values, nu
           const otherValues = otherPeriods
             .map(p => {
               const val = extractNumericValue(financials[p]!.revenue || '');
-              return val !== null && val > 0 ? { period: p, value: val } : null;
+              return val !== null && val > 0 ? { period: p as 'fy3' | 'fy2' | 'fy1' | 'ltm', value: val } : null;
             })
-            .filter((v): v is { period: string; value: number } => v !== null);
+            .filter((v): v is { period: 'fy3' | 'fy2' | 'fy1' | 'ltm'; value: number } => v !== null);
           
           if (otherValues.length > 0) {
             const avgOtherValue = otherValues.reduce((a, b) => a + b.value, 0) / otherValues.length;