sx-git Phase 2: refs — branches/tags/HEAD over persist kv, CAS + reflog (TDD)

Ref value = {:cid} | {:symref}; atomic moves via persist/kv-cas old-value
expect, create-only branches via kv-put-new; bounded symref resolution;
per-ref append-only reflog on the persist log facet. 38/38, total 76/76.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

lib/git/scoreboard.json

@@ -1,8 +1,9 @@
 {
   "suites": {
-    "object": {"pass": 38, "fail": 0}
+    "object": {"pass": 38, "fail": 0},
+    "ref": {"pass": 38, "fail": 0}
   },
-  "total_pass": 38,
+  "total_pass": 76,
   "total_fail": 0,
-  "total": 38
+  "total": 76
 }