feat(ai): enhance AI trace warnings and reason codes system

- Added structured warning system with `AdminAiWarning` type in backend and Flutter
- Implemented detailed reason descriptors with `FlyerReasonDescriptor` for parse and match operations
- Added `legacyWarnings` field to maintain backward compatibility
- Enhanced AI trace service to collect and format warnings with item-level context
- Updated flyer import services to include detailed reason descriptions in responses
- Added Swedish diacritic preservation for cheese variants (Prästost, Herrgårdsost, Grevéost)
- Implemented UTF-8 content validation for AI responses
- Added new reason code definitions in `reason-codes.ts`
- Updated Flutter UI to display structured warnings with severity indicators
- Added error report generation and copy functionality in admin panel
- Added comprehensive test coverage for new warning system and cheese normalization

BREAKING CHANGE: AI trace warnings are now structured objects instead of simple strings

backend/src/flyer-import/services/flyer-normalizer.service.spec.ts

@@ -120,12 +120,28 @@ describe('FlyerNormalizerService', () => {
       const result = service.normalize(items);
 
       expect(result).toHaveLength(3);
-      expect(result.map((item) => item.rawName)).toEqual(['Prästost', 'Herrgårdsost', 'Greveost']);
+      expect(result.map((item) => item.rawName)).toEqual(['Prästost', 'Herrgårdsost', 'Grevéost']);
       expect(result.every((item) => item.brand === 'Arla Ko')).toBe(true);
       expect(result.every((item) => item.categoryHint === 'Hårdost')).toBe(true);
       expect(result[0].parseReasons).toContain('split_cheese_variants');
     });
 
+    it('normalizes PRAST token to Prästost', () => {
+      const items = [{ rawName: 'PRAST, GREVE', brand: 'ARLA KO' }];
+
+      const result = service.normalize(items);
+
+      expect(result.map((item) => item.rawName)).toContain('Prästost');
+    });
+
+    it('normalizes GREVE token to Grevéost', () => {
+      const items = [{ rawName: 'GREVE, PRAST', brand: 'ARLA KO' }];
+
+      const result = service.normalize(items);
+
+      expect(result.map((item) => item.rawName)).toContain('Grevéost');
+    });
+
     it('keeps single cheese item unsplit but normalizes brand/category', () => {
       const items = [
         {
@@ -184,5 +200,20 @@ describe('FlyerNormalizerService', () => {
       expect(result).toHaveLength(1);
       expect(result[0].rawName).toContain('Herrgårdsost');
     });
+
+    it('fixes greveost typo in cheese context and preserves é', () => {
+      const items = [
+        {
+          rawName: 'Greveost skivad',
+          brand: 'Arla Ko',
+        },
+      ];
+
+      const result = service.normalize(items);
+
+      expect(result).toHaveLength(1);
+      expect(result[0].rawName).toContain('Grevéost');
+      expect(result[0].normalizedName).toContain('grevéost');
+    });
   });
 });