chore(example): wire stovepipe orchestrator start controller

[mnoah1]

Wires the start controller into the orchestrator sample app.

Why?

Building out overall structure of https://github.com/uber/submitqueue/blob/main/doc/rfc/stovepipe/workflow.md

What?

• Update main.go to include the newly added start controller from branch below this
• This will create a start controller and begin watching for events on the topic. Also adding the validate topic, as start will insert these

Test Plan

• make local-stovepipe-start
• make local-stovepipe-logs
• Insert a sample message:

docker exec -i stovepipe-mysql-queue-1 mysql -uroot -proot submitqueue -e "INSERT INTO queue_messages (topic, partition_key, id, payload, metadata, created_at, published_at, visible_after, failed_at, failure_count, last_error, original_topic) VALUES ('start', 'github.com/uber/cadence', CONCAT('manual-', CAST(UNIX_TIMESTAMP(NOW(3)) * 1000 AS UNSIGNED)), '{\"uri\":\"git://github.com/uber/cadence/refs/heads/main/abc123def456\",\"partition_key\":\"github.com/uber/cadence\"}', NULL, CAST(UNIX_TIMESTAMP(NOW(3)) * 1000 AS UNSIGNED), CAST(UNIX_TIMESTAMP(NOW(3)) * 1000 AS UNSIGNED), 0, 0, 0, '', '');"
mysql: [Warning] Using a password on the command line interface can be insecure.

• Confirm via logs that the message is receives and enqueues the validate message:

orchestrator-service-1  | 2026-06-16T21:48:54.451Z	INFO	start_controller	start/start.go:91	received change event	{"uri": "git://github.com/uber/cadence/refs/heads/main/abc123def456", "attempt": 1, "partition_key": "github.com/uber/cadence"}
orchestrator-service-1  | 2026-06-16T21:48:54.451Z	DEBUG	queue_mysql.message_store	mysql/message_store.go:72	inserting messages	{"topic": "validate", "count": 1, "visible_after": 0}
orchestrator-service-1  | 2026-06-16T21:48:54.458Z	DEBUG	queue_mysql.message_store	mysql/message_store.go:125	inserted messages	{"topic": "validate", "count": 1}
orchestrator-service-1  | 2026-06-16T21:48:54.458Z	DEBUG	queue_mysql.publisher	mysql/publisher.go:65	published message	{"topic": "validate", "message_id": "git://github.com/uber/cadence/refs/heads/main/abc123def456"}
orchestrator-service-1  | 2026-06-16T21:48:54.458Z	INFO	start_controller	start/start.go:106	published commit to validate	{"uri": "git://github.com/uber/cadence/refs/heads/main/abc123def456", "topic_key": "validate"}
orchestrator-service-1  | 2026-06-16T21:48:54.461Z	DEBUG	consumer/consumer.go:479	message processed successfully	{"controller": "start", "topic_key": "start", "message_id": "manual-1781646534435", "partition_key": "github.com/uber/cadence", "attempt": 1, "elapsed_ms": 6}

• main.go doesn't have tests of its own but we can get some e2e tests in place for stovepipe separately