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/docker-compose.yml

@@ -1,4 +1,36 @@
 services:
+  kafka:
+    image: confluentinc/cp-kafka:7.6.0
+    environment:
+      KAFKA_NODE_ID: 1
+      KAFKA_PROCESS_ROLES: broker,controller
+      KAFKA_LISTENERS: PLAINTEXT://:9092,CONTROLLER://:9093
+      KAFKA_ADVERTISED_LISTENERS: PLAINTEXT://kafka:9092
+      KAFKA_CONTROLLER_QUORUM_VOTERS: 1@kafka:9093
+      KAFKA_CONTROLLER_LISTENER_NAMES: CONTROLLER
+      KAFKA_LISTENER_SECURITY_PROTOCOL_MAP: PLAINTEXT:PLAINTEXT,CONTROLLER:PLAINTEXT
+      KAFKA_OFFSETS_TOPIC_REPLICATION_FACTOR: 1
+      KAFKA_TRANSACTION_STATE_LOG_REPLICATION_FACTOR: 1
+      KAFKA_TRANSACTION_STATE_LOG_MIN_ISR: 1
+      CLUSTER_ID: "MkU3OEVBNTcwNTJENDM2Qg"
+    ports:
+      - "9092:9092"
+    healthcheck:
+      test: ["CMD-SHELL", "kafka-topics --bootstrap-server localhost:9092 --list || exit 1"]
+      interval: 10s
+      timeout: 10s
+      retries: 10
+
+  kafka-init:
+    image: confluentinc/cp-kafka:7.6.0
+    depends_on:
+      kafka:
+        condition: service_healthy
+    entrypoint: ["/bin/sh", "-c"]
+    command: |
+      "kafka-topics --bootstrap-server kafka:9092 --create --if-not-exists --topic ai.recognize.paid --partitions 3 --replication-factor 1 &&
+       kafka-topics --bootstrap-server kafka:9092 --create --if-not-exists --topic ai.recognize.free --partitions 1 --replication-factor 1"
+
   postgres:
     image: postgres:16-alpine
     environment:
@@ -26,9 +58,12 @@ services:
       FIREBASE_CREDENTIALS_FILE: /app/firebase-credentials.json
       JWT_SECRET: local-dev-secret-change-in-prod
       ALLOWED_ORIGINS: http://localhost:3000,http://localhost:9090
+      KAFKA_BROKERS: kafka:9092
     depends_on:
       postgres:
         condition: service_healthy
+      kafka:
+        condition: service_healthy
     volumes:
       - ./firebase-credentials.json:/app/firebase-credentials.json:ro