feat: add dev make target — infra in Docker, server+worker run locally

- Add EXTERNAL listener on port 9093 to Kafka so local processes can connect
- Add KAFKA_BROKERS=localhost:9093 to .env.example
- Add dev/dev-infra-up/dev-infra-down targets to Makefile

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

backend/Makefile

@@ -1,4 +1,4 @@
-.PHONY: run run-worker test test-integration lint migrate-up migrate-down migrate-create migrate-status docker-up docker-down docker-logs docker-logs-worker
+.PHONY: run run-worker dev dev-infra-up dev-infra-down test test-integration lint migrate-up migrate-down migrate-create migrate-status docker-up docker-down docker-logs docker-logs-worker
 
 ifneq (,$(wildcard .env))
   include .env
@@ -12,6 +12,19 @@ run:
 run-worker:
 	go run ./cmd/worker
 
+# Start only infra (postgres, kafka) in Docker, run server + worker locally
+dev: dev-infra-up
+	@trap 'kill 0' INT; \
+	go run ./cmd/server & \
+	go run ./cmd/worker & \
+	wait
+
+dev-infra-up:
+	docker compose up -d postgres kafka kafka-init
+
+dev-infra-down:
+	docker compose stop postgres kafka kafka-init
+
 # Tests
 test:
 	go test ./... -v -race -count=1