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>

migrations/clickhouse/0001_init.sql

@@ -0,0 +1,9 @@
+CREATE TABLE IF NOT EXISTS telemetry.telemetry (
+    device_id   String,
+    zone_id     String,
+    sensor_type String,
+    value       Float64,
+    recorded_at DateTime,
+    received_at DateTime
+) ENGINE = MergeTree()
+ORDER BY (device_id, recorded_at);