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/domain/recognition/job_repository.go

@@ -0,0 +1,125 @@
+package recognition
+
+import (
+	"context"
+	"encoding/json"
+	"time"
+
+	"github.com/food-ai/backend/internal/adapters/ai"
+	"github.com/jackc/pgx/v5/pgxpool"
+)
+
+// JobRepository provides all DB operations on recognition_jobs.
+type JobRepository interface {
+	InsertJob(ctx context.Context, job *Job) error
+	GetJobByID(ctx context.Context, jobID string) (*Job, error)
+	UpdateJobStatus(ctx context.Context, jobID, status string, result *ai.DishResult, errMsg *string) error
+	QueuePosition(ctx context.Context, userPlan string, createdAt time.Time) (int, error)
+	NotifyJobUpdate(ctx context.Context, jobID string) error
+}
+
+// PostgresJobRepository implements JobRepository using a pgxpool.
+type PostgresJobRepository struct {
+	pool *pgxpool.Pool
+}
+
+// NewJobRepository creates a new PostgresJobRepository.
+func NewJobRepository(pool *pgxpool.Pool) *PostgresJobRepository {
+	return &PostgresJobRepository{pool: pool}
+}
+
+// InsertJob inserts a new recognition job and populates the ID and CreatedAt fields.
+func (repository *PostgresJobRepository) InsertJob(queryContext context.Context, job *Job) error {
+	return repository.pool.QueryRow(queryContext,
+		`INSERT INTO recognition_jobs (user_id, user_plan, image_base64, mime_type, lang)
+		 VALUES ($1, $2, $3, $4, $5)
+		 RETURNING id, created_at`,
+		job.UserID, job.UserPlan, job.ImageBase64, job.MimeType, job.Lang,
+	).Scan(&job.ID, &job.CreatedAt)
+}
+
+// GetJobByID fetches a single job by primary key.
+func (repository *PostgresJobRepository) GetJobByID(queryContext context.Context, jobID string) (*Job, error) {
+	var job Job
+	var resultJSON []byte
+
+	queryError := repository.pool.QueryRow(queryContext,
+		`SELECT id, user_id, user_plan, image_base64, mime_type, lang, status,
+		        result, error, created_at, started_at, completed_at
+		 FROM recognition_jobs WHERE id = $1`,
+		jobID,
+	).Scan(
+		&job.ID, &job.UserID, &job.UserPlan,
+		&job.ImageBase64, &job.MimeType, &job.Lang, &job.Status,
+		&resultJSON, &job.Error, &job.CreatedAt, &job.StartedAt, &job.CompletedAt,
+	)
+	if queryError != nil {
+		return nil, queryError
+	}
+
+	if resultJSON != nil {
+		var dishResult ai.DishResult
+		if unmarshalError := json.Unmarshal(resultJSON, &dishResult); unmarshalError == nil {
+			job.Result = &dishResult
+		}
+	}
+
+	return &job, nil
+}
+
+// UpdateJobStatus transitions a job to a new status and records the result or error.
+func (repository *PostgresJobRepository) UpdateJobStatus(
+	queryContext context.Context,
+	jobID, status string,
+	result *ai.DishResult,
+	errMsg *string,
+) error {
+	var resultJSON []byte
+	if result != nil {
+		marshalledBytes, marshalError := json.Marshal(result)
+		if marshalError != nil {
+			return marshalError
+		}
+		resultJSON = marshalledBytes
+	}
+
+	switch status {
+	case JobStatusProcessing:
+		_, updateError := repository.pool.Exec(queryContext,
+			`UPDATE recognition_jobs SET status = $1, started_at = now() WHERE id = $2`,
+			status, jobID,
+		)
+		return updateError
+	default:
+		_, updateError := repository.pool.Exec(queryContext,
+			`UPDATE recognition_jobs
+			 SET status = $1, result = $2, error = $3, completed_at = now()
+			 WHERE id = $4`,
+			status, resultJSON, errMsg, jobID,
+		)
+		return updateError
+	}
+}
+
+// QueuePosition counts jobs ahead of createdAt in the same plan's queue.
+func (repository *PostgresJobRepository) QueuePosition(
+	queryContext context.Context,
+	userPlan string,
+	createdAt time.Time,
+) (int, error) {
+	var position int
+	queryError := repository.pool.QueryRow(queryContext,
+		`SELECT COUNT(*) FROM recognition_jobs
+		 WHERE status IN ('pending', 'processing')
+		   AND user_plan = $1
+		   AND created_at < $2`,
+		userPlan, createdAt,
+	).Scan(&position)
+	return position, queryError
+}
+
+// NotifyJobUpdate sends a PostgreSQL NOTIFY on the job_update channel.
+func (repository *PostgresJobRepository) NotifyJobUpdate(queryContext context.Context, jobID string) error {
+	_, notifyError := repository.pool.Exec(queryContext, `SELECT pg_notify('job_update', $1)`, jobID)
+	return notifyError
+}