docs: sync from backend cdc8df1 + frontend a5dd48e + scanner 8fee27e — AMN Pay Scanner

- Activity Log: new entry for AMN Pay Scanner implementation
- Environment Variables: document AMN_SCANNER_URL, AMN_SCANNER_WEBHOOK_SECRET, AMN_SCANNER_DEFAULT
- PRD status table: mark all components implemented

07 - Development/Environment Variables.md

@@ -326,6 +326,11 @@ SWEEP_MASTER_PRIVKEY=
 SWEEP_GAS_MIN_BNB=0.001
 SWEEP_GAS_TOP_UP_BNB=0.002
 
+# AMN Pay Scanner (replaces Request Network for pay-in detection)
+AMN_SCANNER_URL=
+AMN_SCANNER_WEBHOOK_SECRET=
+AMN_SCANNER_DEFAULT=false
+
 # OAuth
 GOOGLE_CLIENT_ID=
 ```