Implement ingest-service: MQTT -> ClickHouse (batched) + RabbitMQ event

Subscribes to devices/+/telemetry, validates payloads, buffers writes into
ClickHouse (flush on size or interval), and emits a per-reading event on
RabbitMQ for rule-engine-service to consume later. Adds the initial Postgres
and ClickHouse schema migrations, a Dockerfile, and wires the service into
docker-compose. Verified end-to-end via docker compose + mosquitto_pub: row
lands in ClickHouse and the event reaches the telemetry.new_reading queue.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

.env.example

@@ -32,6 +32,13 @@ MQTT_PORT=1883
 # --- device-control-service (gRPC) ---
 DEVICE_CONTROL_GRPC_PORT=50051
 
+# --- ingest-service ---
+INGEST_MQTT_CLIENT_ID=ingest-service
+INGEST_MQTT_TOPIC=devices/+/telemetry
+INGEST_BATCH_MAX_SIZE=500
+INGEST_BATCH_FLUSH_INTERVAL=5s
+INGEST_BATCH_FLUSH_TIMEOUT=10s
+
 # --- Laravel app (stage 2) ---
 APP_KEY=
 APP_URL=http://localhost:8000