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.

.env.example

@@ -67,6 +67,11 @@ PCM_RETURN_ADDRESS=
 # PCM_RETURN_CITY=
 # PCM_RETURN_STATE=
 # PCM_RETURN_ZIP=
+# Fallback per-piece dollars when PCM design payload has no pricing[].
+# PCM_POSTCARD_PRICE_FIRSTCLASS=0.89
+# PCM_POSTCARD_PRICE_STANDARD=0.55
+# Occupant list type for carrier-route counts (GET /list/types).
+# PCM_LIST_TYPE=IRL
 
 # Social
 # LinkedIn / Instagram App ID + Secret: Portal → Social accounts (not env).