persist: global commit ordering across streams + 11 tests

global.sx: persist/gappend records a pointer in a reserved $global index whose
seq is the global commit position; read-global/project-global replay every
event in commit order; global-from for incremental consumers. Opt-in (plain
append untouched); $-prefixed streams now reserved + hidden from the public
catalog (streams-all reveals them). Gives feed its unified timeline.
Deterministic across restart. 191/191.

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 catalog query batch upcast idempotency recovery)
+SUITES=(event log kv project subscribe concurrency snapshot compaction durable blob view cas catalog query batch upcast idempotency global recovery)
 
 OUT_JSON="lib/persist/scoreboard.json"
 OUT_MD="lib/persist/scoreboard.md"
@@ -43,6 +43,7 @@ run_suite() {
 (load "lib/persist/batch.sx")
 (load "lib/persist/upcast.sx")
 (load "lib/persist/idempotency.sx")
+(load "lib/persist/global.sx")
 (load "lib/persist/subscribe.sx")
 (load "lib/persist/api.sx")
 (epoch 2)