[fix] register sync_branch in VERBS_WITHOUT_TRACING

sync_branch (B1, 250be5c2) is a git-only rebase+force-push verb (composes=(),
no DB transition, side_effects=()) but was never registered in the tracing
parity tables, so test_every_intent_verb_has_a_tracing_decision failed.
Mirrors open_pr: a mechanical git op with inline preconditions (ownership),
no journal/plan rationale required.

roboco/foundation/policy/tracing.py

@@ -391,6 +391,9 @@ VERBS_WITHOUT_TRACING: frozenset[str] = frozenset(
         "claim_doc_task",
         # open_pr is a mechanical push+open; preconditions are inline.
         "open_pr",
+        # sync_branch is a git-only rebase+force-push through the gate; no DB
+        # state change, no journal/plan rationale (mirrors open_pr).
+        "sync_branch",
     }
 )