persist: stream catalog — enumerate streams + 10 tests

New backend op :streams (from seq high-water marks, so compacted streams still
list), threaded through mem-backend + durable serve/io-backend. catalog.sx:
persist/streams, stream-count, stream-exists?, total-events. 143/143.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

lib/persist/conformance.sh

@@ -13,7 +13,7 @@ if [ ! -x "$SX_SERVER" ]; then
   exit 1
 fi
 
-SUITES=(event log kv project subscribe concurrency snapshot compaction durable blob view cas recovery)
+SUITES=(event log kv project subscribe concurrency snapshot compaction durable blob view cas catalog recovery)
 
 OUT_JSON="lib/persist/scoreboard.json"
 OUT_MD="lib/persist/scoreboard.md"
@@ -38,6 +38,7 @@ run_suite() {
 (load "lib/persist/durable.sx")
 (load "lib/persist/blob.sx")
 (load "lib/persist/view.sx")
+(load "lib/persist/catalog.sx")
 (load "lib/persist/subscribe.sx")
 (load "lib/persist/api.sx")
 (epoch 2)