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/app.go

@@ -0,0 +1,27 @@
+package main
+
+import (
+	"context"
+	"net/http"
+
+	"github.com/food-ai/backend/internal/domain/recognition"
+)
+
+// App bundles the HTTP handler with background services that need lifecycle management.
+type App struct {
+	handler    http.Handler
+	workerPool *recognition.WorkerPool
+	sseBroker  *recognition.SSEBroker
+}
+
+// ServeHTTP implements http.Handler.
+func (application *App) ServeHTTP(responseWriter http.ResponseWriter, request *http.Request) {
+	application.handler.ServeHTTP(responseWriter, request)
+}
+
+// Start launches the SSE broker's LISTEN loop and the worker pool goroutines.
+// Call this once before the HTTP server begins accepting connections.
+func (application *App) Start(applicationContext context.Context) {
+	application.sseBroker.Start(applicationContext)
+	application.workerPool.Start(applicationContext)
+}