Add e-mail system: send applications, receive & reply to responses

Send the complete application (body + generated attachments) to a
user-entered address via authenticated SMTP submission through the
account's own server, so it applies DKIM and uses its reputable IP/PTR —
required for deliverability here (domain publishes SPF -all, DMARC
p=reject). From/Return-Path stay aligned on the sending domain.

Reply e-mails are polled over IMAP, parsed, stored and matched to the
right application (via In-Reply-To/References, then sender address);
their attachments are saved and downloadable. The detail page gains a
correspondence thread with compose, threaded reply, and an AI-drafted
reply the user can edit before sending.

New: lib/mailer.js (nodemailer + imapflow + mailparser), generateEmailReply
in lib/documents.js, emails/email_anhaenge/app_state tables, background
poller + manual fetch. Credentials come from MAIL_* env vars (.env, not
committed / not in the image).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

.env.example

@@ -9,3 +9,18 @@ OLLAMA_API_KEY=
 
 # Optional – anderer Host (z. B. lokale Ollama-Instanz: http://localhost:11434)
 # OLLAMA_HOST=https://ollama.com
+
+# --- E-Mail (SMTP-Versand + IMAP-Empfang) ---
+# Versand läuft über die authentifizierte Submission des eigenen Mailservers,
+# damit dieser DKIM signiert und die reputable IP/PTR nutzt (SPF/DMARC-Alignment).
+# Ohne diese Angaben ist der E-Mail-Teil deaktiviert.
+MAIL_HOST=mail.example.com
+MAIL_SMTP_PORT=587
+MAIL_IMAP_PORT=993
+MAIL_USER=name@example.com
+MAIL_PASSWORD=
+MAIL_FROM_NAME=Vorname Nachname
+MAIL_FROM=name@example.com
+# IMAP-Postfach + Abrufintervall (ms) für neue Antwortmails
+MAIL_IMAP_MAILBOX=INBOX
+MAIL_POLL_MS=180000