Add PCM carrier-route postcard pick-and-send (#15)

## Summary
Closes #15.
- Let compose target mailing-list contacts or 1–2 USPS carrier routes, with household count and estimated cost shown before save.
- Place selected routes through PCM list-count orders instead of importing occupant addresses into Contacts.

site/messaging/tasks.py

@@ -18,7 +18,9 @@ def send_campaign_message(message_id: str) -> None:
 
     campaign = message.campaign
 
-    if not contact_may_receive(message.contact, message.channel):
+    if message.contact_id is None:
+        pass
+    elif not contact_may_receive(message.contact, message.channel):
         message.status = Message.Status.SUPPRESSED
         message.error = "Contact opted out or suppressed"
         message.save(update_fields=["status", "error", "updated_at"])