fix(mnesia): apply dump_log_write_threshold before mnesia start.

change_config rejected the key; set_env + verify enables the IFT ceiling ladder. Refs EventHub/EventHubBack#30 Refs EventHub/EventHubBack#34

Co-authored-by: Cursor <cursoragent@cursor.com>

test/tsung/eventhub_ift_stress_hold.xml

@@ -3,13 +3,13 @@
 <!--
   IFT controlled hold: поиск устойчивого (зелёного) потолка hot-path.
   Пул: ift-users.csv. Mix browse 70% / write 30%.
-  maxusers=300; ladder 0.2→0.1→0.05→0.035; hold ≥2 мин.
+  maxusers=100 (use_controller_vm); ladder 0.2→0.1→0.05→0.035; hold ≥2 мин.
   thinktime value=1 (целые секунды) — темп без connect-storm.
   Критерий 2A: error >1% ИЛИ mean >500 ms.
 -->
 <tsung loglevel="notice" version="1.0">
     <clients>
-        <client host="localhost" use_controller_vm="true" maxusers="300"/>
+        <client host="localhost" use_controller_vm="true" maxusers="100"/>
     </clients>
 
     <servers>