feat: async dish recognition (Kafka/Watermill/SSE) + remove Wire + consolidate migrations

Async recognition pipeline:
- POST /ai/recognize-dish → 202 {job_id, queue_position, estimated_seconds}
- GET /ai/jobs/{id}/stream — SSE stream: queued → processing → done/failed
- Kafka topics: ai.recognize.paid (3 partitions) + ai.recognize.free (1 partition)
- 5-worker WorkerPool with priority loop (paid consumers first)
- SSEBroker via PostgreSQL LISTEN/NOTIFY
- Kafka adapter migrated from franz-go to Watermill (watermill-kafka/v2)
- Docker Compose: added Kafka + Zookeeper + kafka-init service
- Flutter: recognition_service.dart uses SSE; home_screen shows live job status

Remove google/wire (archived):
- Deleted wire.go (wireinject spec) and wire_gen.go
- Added cmd/server/init.go — plain Go manual DI, same initApp() logic
- Removed github.com/google/wire from go.mod

Consolidate migrations:
- Merged 001_initial_schema + 002_seed_data + 003_recognition_jobs into single 001_initial_schema.sql
- Deleted 002_seed_data.sql and 003_recognition_jobs.sql

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

backend/internal/infra/config/config.go

@@ -24,6 +24,9 @@ type Config struct {
 	// External APIs
 	OpenAIAPIKey  string `envconfig:"OPENAI_API_KEY" required:"true"`
 	PexelsAPIKey  string `envconfig:"PEXELS_API_KEY" required:"true"`
+
+	// Kafka
+	KafkaBrokers []string `envconfig:"KAFKA_BROKERS" default:"kafka:9092"`
 }
 
 func Load() (*Config, error) {

backend/internal/infra/server/server.go

@@ -120,6 +120,8 @@ func NewRouter(
 			r.Post("/recognize-receipt", recognitionHandler.RecognizeReceipt)
 			r.Post("/recognize-products", recognitionHandler.RecognizeProducts)
 			r.Post("/recognize-dish", recognitionHandler.RecognizeDish)
+			r.Get("/jobs/{id}", recognitionHandler.GetJob)
+			r.Get("/jobs/{id}/stream", recognitionHandler.GetJobStream)
 			r.Post("/generate-menu", menuHandler.GenerateMenu)
 		})
 	})