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/cmd/server/main.go

@@ -48,14 +48,16 @@ func run() error {
 	}
 	slog.Info("languages loaded", "count", len(locale.Languages))
 
-	router, initError := initRouter(appConfig, pool)
+	application, initError := initApp(appConfig, pool)
 	if initError != nil {
-		return fmt.Errorf("init router: %w", initError)
+		return fmt.Errorf("init app: %w", initError)
 	}
 
+	application.Start(applicationContext)
+
 	httpServer := &http.Server{
 		Addr:         fmt.Sprintf(":%d", appConfig.Port),
-		Handler:      router,
+		Handler:      application,
 		ReadTimeout:  10 * time.Second,
 		WriteTimeout: 120 * time.Second, // menu generation can take ~60s
 		IdleTimeout:  60 * time.Second,