feat(flyer-import): integrate AI-based flyer parsing with image support

- Add support for PNG, JPEG, and WebP image formats in flyer import
- Replace external importer service with internal AI-based parsing pipeline
- Add new services: TextExtractorService, AiFlyerParserService, FlyerNormalizerService
- Integrate Mistral AI, pdf-parse, and tesseract.js dependencies
- Add quality confidence indicators and warning panels in Flutter UI
- Update package.json with new dependencies and transform ignore patterns
- Add documentation for flyer importer system
- Add Kilo AI planning file for Happy Island project

BREAKING CHANGE: Flyer import now uses internal AI parsing instead of external importer service

backend/package.json

@@ -18,6 +18,7 @@
     "test:watch": "jest --watch"
   },
   "dependencies": {
+    "@mistralai/mistralai": "^0.5.0",
     "@nestjs/common": "^11.1.19",
     "@nestjs/core": "^11.1.19",
     "@nestjs/jwt": "^11.0.2",
@@ -32,10 +33,12 @@
     "multer": "^2.1.1",
     "passport": "^0.7.0",
     "passport-jwt": "^4.0.1",
+    "pdf-parse": "^1.1.1",
     "prisma": "6.12.0",
     "reflect-metadata": "^0.2.2",
     "rxjs": "^7.8.1",
     "sharp": "^0.33.5",
+    "tesseract.js": "^5.1.1",
     "uuid": "^11.1.0"
   },
   "devDependencies": {
@@ -48,6 +51,7 @@
     "@types/multer": "^1.4.12",
     "@types/node": "^22.15.29",
     "@types/passport-jwt": "^4.0.1",
+    "@types/pdf-parse": "^1.1.5",
     "@types/supertest": "^7.2.0",
     "@types/uuid": "^10.0.0",
     "@typescript-eslint/eslint-plugin": "^8.46.2",
@@ -67,6 +71,9 @@
       "js",
       "json",
       "ts"
+    ],
+    "transformIgnorePatterns": [
+      "node_modules/(@mistralai)"
     ]
   }
 }