feat: implement Iteration 3 — product/receipt/dish recognition

Backend:
- gemini/client.go: refactor to shared callGroq transport; add
  generateVisionContent using llama-3.2-11b-vision-preview model
- gemini/recognition.go: RecognizeReceipt, RecognizeProducts,
  RecognizeDish (vision), ClassifyIngredient (text); shared parseJSON helper
- ingredient/repository.go: add FuzzyMatch (wraps Search, returns best hit)
- recognition/handler.go: POST /ai/recognize-receipt, /ai/recognize-products,
  /ai/recognize-dish; enrichItems with fuzzy match + AI classify fallback;
  parallel multi-image processing with deduplication
- server.go + main.go: wire recognition handler under /ai routes

Flutter:
- pubspec.yaml: add image_picker ^1.1.0
- AndroidManifest.xml: add CAMERA and READ_EXTERNAL_STORAGE permissions
- Info.plist: add NSCameraUsageDescription and NSPhotoLibraryUsageDescription
- recognition_service.dart: RecognitionService wrapping /ai/* endpoints;
  RecognizedItem, ReceiptResult, DishResult models
- scan_screen.dart: mode selector (receipt / products / dish / manual);
  image source picker; loading overlay; navigates to confirm or dish screen
- recognition_confirm_screen.dart: editable list of recognized items;
  inline qty/unit editing; swipe-to-delete; batch-add to pantry
- dish_result_screen.dart: dish name, KBZHU breakdown, similar dishes chips
- app_router.dart: /scan, /scan/confirm, /scan/dish routes (no bottom nav)
- products_screen.dart: FAB now shows bottom sheet with Manual / Scan options

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

backend/internal/server/server.go

@@ -8,6 +8,7 @@ import (
 	"github.com/food-ai/backend/internal/ingredient"
 	"github.com/food-ai/backend/internal/middleware"
 	"github.com/food-ai/backend/internal/product"
+	"github.com/food-ai/backend/internal/recognition"
 	"github.com/food-ai/backend/internal/recommendation"
 	"github.com/food-ai/backend/internal/savedrecipe"
 	"github.com/food-ai/backend/internal/user"
@@ -23,6 +24,7 @@ func NewRouter(
 	savedRecipeHandler *savedrecipe.Handler,
 	ingredientHandler *ingredient.Handler,
 	productHandler *product.Handler,
+	recognitionHandler *recognition.Handler,
 	authMiddleware func(http.Handler) http.Handler,
 	allowedOrigins []string,
 ) *chi.Mux {
@@ -71,6 +73,12 @@ func NewRouter(
 			r.Put("/{id}", productHandler.Update)
 			r.Delete("/{id}", productHandler.Delete)
 		})
+
+		r.Route("/ai", func(r chi.Router) {
+			r.Post("/recognize-receipt", recognitionHandler.RecognizeReceipt)
+			r.Post("/recognize-products", recognitionHandler.RecognizeProducts)
+			r.Post("/recognize-dish", recognitionHandler.RecognizeDish)
+		})
 	})
 
 	return r