Enhance SMTP configuration in docker-compose and email handler

- Updated docker-compose.yml to include optional SMTP settings with comments for clarity on configuration.
- Modified email-handler.ts to prioritize FROM_EMAIL for the sender address, falling back to SMTP_USER or ADMIN_EMAIL if not set, improving email handling flexibility.

server.js

@@ -25,7 +25,7 @@ app.use((req, res, next) => {
   if (process.env.ENABLE_SSR_CSP === '1') {
     res.setHeader(
       'Content-Security-Policy',
-      "default-src 'self' https://365devnet.eu https://*.365devnet.eu; " +
+      "default-src 'self' https://365devnet.eu https://*.365devnet.eu https://chat.365devnet.eu; " +
       "script-src 'self' 'unsafe-inline' 'wasm-unsafe-eval' https://chat.365devnet.eu; " +
       "style-src 'self' 'unsafe-inline'; " +
       "img-src 'self' data: https: blob:; " +