chore(domain): migrate to nexusautoparts.com.mx

- Update Nginx config:
  - nexusautoparts.com.mx -> POS (port 5001)
  - admin.nexusautoparts.com.mx -> Dashboard (port 5000)
  - nexus.consultoria-as.com -> legacy redirect (dashboard)
  - Add redirect / -> /pos/login for main domain
- Update domain references in code:
  - capacitor.config.json (mobile apps)
  - pos/mobile/README.md
  - pos/config.py SMTP_FROM
- Add Caddy config docs for reverse proxy VM (192.168.10.74)

docs/CADDY_CONFIG.md

@@ -0,0 +1,32 @@
+# Caddy Config for nexusautoparts.com.mx
+
+## VM with Caddy: 192.168.10.74
+## VM with POS/Dashboard: 192.168.10.91
+
+Add this to `/etc/caddy/Caddyfile` on the Caddy VM (192.168.10.74):
+
+```caddyfile
+# Main POS domain
+nexusautoparts.com.mx, www.nexusautoparts.com.mx {
+    reverse_proxy 192.168.10.91:80
+}
+
+# Admin dashboard subdomain
+admin.nexusautoparts.com.mx {
+    reverse_proxy 192.168.10.91:80
+}
+
+# Legacy domain (optional, redirect or keep)
+nexus.consultoria-as.com {
+    reverse_proxy 192.168.10.91:80
+}
+```
+
+Then reload Caddy:
+```bash
+sudo systemctl reload caddy
+# or
+sudo caddy reload --config /etc/caddy/Caddyfile
+```
+
+Caddy will automatically obtain Let's Encrypt certificates for all domains.