Refactor kafka to pure Go (franz-go), fix DBC stubs, update Dockerfile

pkg/kafka/README.md

@@ -0,0 +1,83 @@
+# Kafka Package
+
+Pure Go Kafka client using [franz-go](https://github.com/twmb/franz-go).
+
+## Why franz-go?
+
+- Pure Go - no CGO, no librdkafka dependency
+- Builds to static binaries, works with scratch/distroless images
+- Well-maintained, performant, full Kafka protocol support
+
+## Usage
+
+### Producer
+
+```go
+producer, err := kafka.NewProducer(ctx)
+if err != nil {
+    return err
+}
+defer producer.Close()
+
+// Sync produce
+err = producer.Produce("my-topic", "key", myPayload, nil)
+
+// Async produce
+err = producer.ProduceToChannel("my-topic", "key", myPayload)
+```
+
+### Consumer
+
+```go
+consumer, err := kafka.NewConsumer("my-service")
+if err != nil {
+    return err
+}
+defer consumer.Stop()
+
+// With handler
+consumer.Consume([]string{"topic1", "topic2"}, func(key, value []byte) error {
+    // process message
+    return nil
+})
+
+// Or with channel
+events := make(chan *kafka.Message)
+go consumer.ConsumeToChannel([]string{"topic1"}, events)
+for msg := range events {
+    // process msg
+}
+```
+
+### Admin
+
+```go
+// Ensure topics exist (creates if missing)
+kafka.EnsureTopicsExist([]string{"topic1", "topic2"})
+```
+
+## Configuration
+
+All config via environment variables:
+
+| Variable | Default | Description |
+|----------|---------|-------------|
+| `KAFKA_HOSTS` | `localhost:9092` | Broker addresses (comma-separated) |
+| `KAFKA_SECURITY_PROTOCOL` | `plaintext` | `plaintext`, `ssl`, `sasl_plaintext`, `sasl_ssl` |
+| `KAFKA_SASL_MECHANISMS` | `` | `PLAIN`, `SCRAM-SHA-256`, `SCRAM-SHA-512` |
+| `KAFKA_SASL_USERNAME` | `` | SASL username |
+| `KAFKA_SASL_PASSWORD` | `` | SASL password |
+| `KAFKA_SESSION_TIMEOUT_MS` | `45000` | Consumer session timeout |
+| `KAFKA_HEARTBEAT_INTERVAL_MS` | `3000` | Consumer heartbeat interval |
+| `KAFKA_ENABLE_AUTO_COMMIT` | `true` | Auto-commit offsets |
+| `KAFKA_AUTO_COMMIT_INTERVAL_MS` | `5000` | Auto-commit interval |
+| `KAFKA_TIMEOUT` | `10000` | Poll timeout (ms) |
+| `KAFKA_TOPIC_PARTITIONS` | `1` | Default partitions for new topics |
+| `KAFKA_TOPIC_REPLICATION_FACTOR` | `1` | Default replication factor |
+
+## Migration from confluent-kafka-go
+
+The interfaces are compatible. Main changes:
+- `*kafka.Message` → `*kafka.Message` (our wrapper type)
+- `kafka.TopicPartition` → `kafka.TopicPartition` (our type)
+- No more CGO build tags or librdkafka deps