BREAKING: move Kafka reporting chain from trace-collector to trace-mgr
trace-collector now only collects and serializes Spans, delivering (topic, spanJson) cross-module via reflection. Buffering, sending, and shutdown move to trace-mgr (report package: SpanReport / SpanBuffer / KafkaReporter, poll-pull + batching). kafka-clients moves from trace-collector to trace-mgr; Guava removed from collector. Adds Rule.reportTopic and KafkaProducerListener recursion guard.
(openspec: kafka-reporter-migration)