Fix contact form: use host networking to reach Proton Bridge SMTP

Both containers now run in network_mode: host so the API can connect
directly to Proton Bridge on 127.0.0.1:1025. The pfSense search domain
(home.arpa) was leaking into Docker DNS and causing NXDOMAIN failures
for inter-container hostnames. Host networking bypasses this entirely.

- docker-compose: both services use network_mode: host
- nginx: listen on 8080 (was 80), proxy /api/ to 127.0.0.1:3001
- server.js: allow self-signed TLS cert from Proton Bridge

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

docker-compose.yml

@@ -2,8 +2,7 @@ services:
   frontend:
     build: ./frontend
     container_name: www-kenjim-frontend
-    ports:
-      - "8080:80"
+    network_mode: host
     depends_on:
       - api
     restart: always
@@ -11,5 +10,6 @@ services:
   api:
     build: ./backend
     container_name: www-kenjim-api
+    network_mode: host
     env_file: .env
     restart: always