docs(plugin): clarify session-only Auto-Tell-Tab invariant (F2.3)

Expands the one-liner above Plugin.cs:167-168 to spell out *why* the
RemoveAll runs before AutoTellTabsService.Initialize: tells are
typically privacy-filtered, so resurrecting a tab from a crashed
session would trigger DB reconstruction on the next load. Also links
to the TEST-MIRROR pin in the Build-Suite for future readers.

HellionChat/Plugin.cs

@@ -164,7 +164,11 @@ public sealed class Plugin : IAsyncDalamudPlugin
             );
         }
 
-        // Drop session-only Auto-Tell-Tabs that a previous crash may have persisted.
+        // Auto-Tell-Tabs are session-only: their messages are usually
+        // privacy-filtered and resurrecting an empty tab from a crashed
+        // session would trigger DB-reconstruction on the next load. The
+        // TempTabCounter then re-pegs the snapshot from the stripped list in
+        // AutoTellTabsService.Initialize. (F2.3 — TEST-MIRROR in Build-Suite.)
         Config.Tabs.RemoveAll(t => t.IsTempTab);
 
         LanguageChanged(Interface.UiLanguage);