032: fix 2 critical QA issues — missing endregion + Tombstone dead helpers

C1: _llm_call.py — added missing #endregion _split_and_retry (violated INV_3)
C2: dashboards/_helpers.py — sync _find_dashboard_id_by_slug and
    _resolve_dashboard_id_from_ref typed Tombstone per INV_6 (dead code,
    callers use _async versions from git/_helpers.py)

backend/src/plugins/translate/_llm_call.py

@@ -278,6 +278,8 @@ class LLMTranslationService:
                 "skipped": left["skipped"] + right["skipped"],
                 "retries": retries + left.get("retries", 0) + right.get("retries", 0)}
 
+    # #endregion _split_and_retry
+
     # #region _try_recover_partial [C:3] [TYPE Function] [SEMANTICS translate, llm, recovery]
     # @BRIEF Try to recover translated rows from a truncated LLM response.
     #        Saves recovered rows as SUCCESS records. Returns set of recovered row_index values.