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>

frontend/nginx.conf

@@ -1,19 +1,16 @@
 server {
-    listen 80;
+    listen 8080;
     root /usr/share/nginx/html;
     index index.html;
 
-    # SPA routing — return index.html for all non-file routes
     location / {
         try_files $uri $uri/ /index.html;
     }
 
-    # Proxy API calls to the backend container
-    # Use Docker's internal DNS resolver so upstream resolves at request time
-    resolver 127.0.0.11 valid=10s;
-    set $api http://api:3001;
+    # Both containers share host network; api is on localhost:3001.
+    # Trailing slash strips the /api/ prefix before forwarding.
     location /api/ {
-        proxy_pass         $api/;
+        proxy_pass         http://127.0.0.1:3001/;
         proxy_set_header   Host              $host;
         proxy_set_header   X-Real-IP         $remote_addr;
         proxy_set_header   X-Forwarded-For   $proxy_add_x_forwarded_for;