fix(migrate): drop WhatsApp LID dual-row migration step

Remove step 2d (whatsapp-resolve-lids.ts) which pre-created duplicate
messaging_groups rows keyed by @lid alongside the phone-keyed rows.
This caused split sessions — the same contact got separate sessions
depending on which JID format arrived.

With the Baileys v7 upgrade (PR #2259 on channels), the adapter
resolves every LID to a phone JID via extractAddressingContext before
the message reaches the router, making dual rows unnecessary.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

migrate-v2.sh

@@ -408,20 +408,12 @@ else
     fi
   done
 
-  # 2d. WhatsApp LID resolution. After whatsapp is installed (so Baileys
-  # is on disk) and auth files have been copied (so we can connect with
-  # the migrated identity), boot Baileys briefly to learn LID↔phone
-  # mappings during initial sync, then write paired LID-keyed
-  # messaging_groups. Best-effort: any failure degrades to runtime
-  # approval flow, which the WA adapter's isMention=true on DMs handles.
-  for ch in "${SELECTED_CHANNELS[@]}"; do
-    if [ "$ch" = "whatsapp" ]; then
-      run_step "2d-whatsapp-lids" \
-        "Resolve WhatsApp LIDs for migrated DMs" \
-        "setup/migrate-v2/whatsapp-resolve-lids.ts"
-      break
-    fi
-  done
+  # 2d. (Removed) WhatsApp LID resolution was previously needed because the
+  # v6 adapter couldn't reliably translate LID→phone JIDs, so the migration
+  # pre-created dual messaging_groups rows. With Baileys v7, the adapter
+  # resolves LIDs via extractAddressingContext + signalRepository.lidMapping
+  # on every inbound message, so dual rows are unnecessary and were causing
+  # split sessions.
 fi
 
 echo