perf(clickhouse): enable LZ4 client compression on inserts

cmd/bench/clickhouse-compression/README.md

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+# ClickHouse Compression Bench
+
+One-off bench used to validate enabling LZ4 client compression (#909 / #911).
+
+Alternates `Compression` off / LZ4 / ZSTD against the same CH instance, tags
+each insert with a `query_id`, then pulls exact wire bytes from
+`system.query_log.ProfileEvents['NetworkReceiveBytes']` for comparison.
+
+## Run
+
+```bash
+# Local dev CH (build/dev/deps/compose.yml --profile clickhouse)
+CLICKHOUSE_ADDR=localhost:29000 \
+CLICKHOUSE_USERNAME=outpost \
+CLICKHOUSE_PASSWORD=outpost \
+CLICKHOUSE_DATABASE=outpost \
+  go run ./cmd/bench/clickhouse-compression --batches=5 --rows=100000
+
+# Remote (CH Cloud, TLS)
+CLICKHOUSE_ADDR=<host>:9440 \
+CLICKHOUSE_USERNAME=<user> \
+CLICKHOUSE_PASSWORD=<pass> \
+CLICKHOUSE_DATABASE=<db> \
+CLICKHOUSE_TLS_ENABLED=true \
+  go run ./cmd/bench/clickhouse-compression --batches=10 --rows=10000
+```
+
+## Flags
+
+| flag | default | meaning |
+|---|---|---|
+| `--batches` | 5 | runs per mode |
+| `--rows` | 10000 | rows per batch |
+| `--modes` | `off,lz4,zstd` | subset of codecs to test |
+| `--keep` | false | keep the throwaway table on exit |
+
+The bench creates a `bench_compression_<rand>` MergeTree table and drops it
+on exit (no schema/migration dependency). Payload is ~700-byte JSON
+representative of event bodies.