mailu: enable central database, improve token creation task, and add migration guide

- Enabled central_database in Mailu config
- Improved API token creation task:
  * use curl -f to fail on HTTP errors
  * added explicit failed_when and changed_when conditions
- Adjusted docker-compose template spacing for readability
- Made logging level configurable (DEBUG when MODE_DEBUG is set)
- Added new documentation Move_Domain.md explaining safe procedure for migrating mailboxes to a new domain

roles/web-app-mailu/docs/Move_Domain.md

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+# 📖 **How to Migrate Mailboxes to a New Domain in Mailu**
+
+When changing the primary email domain (e.g., from `cymais.cloud` to `infinito.nexus`), it is **not enough** to simply rename mailbox directories on disk. Mailu manages domain and user records in its internal database, and Dovecot maintains index files inside each Maildir. A blind rename will lead to login failures, rejected mail, or corrupted mail indices.
+
+This guide explains the **safe procedure** for migrating user mailboxes to a new domain.
+
+---
+
+## 🔴 Why renaming folders directly does not work
+
+* Mailu keeps **domains, users, and aliases** in the `admin_data` database. If you rename folders only, Mailu will not recognize the new accounts.
+* Dovecot generates `.dovecot.index*` and `dovecot-uidlist` files in each mailbox. These must be rebuilt when moving mailboxes; otherwise, users may see missing or broken mail.
+* Postfix will refuse to deliver or relay messages for unknown domains.
+
+---
+
+## ✅ Correct migration procedure
+
+### 1. Add the new domain and users in Mailu
+
+Use the Mailu CLI inside the `admin` container:
+
+```bash
+# Add new domain
+docker compose exec admin flask mailu domain add infinito.nexus
+
+# Add new user (repeat for each account)
+docker compose exec admin flask mailu user kevinveenbirkenbach infinito.nexus 'NEW_PASSWORD'
+```
+
+---
+
+### 2. Copy or move existing Maildir contents
+
+Instead of renaming, copy the entire Maildir from the old domain to the new one:
+
+```bash
+rsync -aHAX --numeric-ids \
+  /var/lib/docker/volumes/mailu_dovecot_mail/_data/kevinveenbirkenbach@cymais.cloud/ \
+  /var/lib/docker/volumes/mailu_dovecot_mail/_data/kevinveenbirkenbach@infinito.nexus/
+```
+
+---
+
+### 3. Remove old Dovecot index files
+
+Ensure that Dovecot rebuilds indices cleanly:
+
+```bash
+find /var/lib/docker/volumes/mailu_dovecot_mail/_data/kevinveenbirkenbach@infinito.nexus -type f -name '.dovecot*' -delete
+find /var/lib/docker/volumes/mailu_dovecot_mail/_data/kevinveenbirkenbach@infinito.nexus -type f -name 'dovecot-uidlist*' -delete
+```
+
+---
+
+### 4. Fix file permissions
+
+Make sure all mailbox files belong to the `mail:mail` user/group:
+
+```bash
+chown -R mail:mail /var/lib/docker/volumes/mailu_dovecot_mail/_data/kevinveenbirkenbach@infinito.nexus
+```
+
+---
+
+### 5. Restart services and test login
+
+After copying, restart Mailu services (or at least `imap` and `smtp`) and confirm that users can log in with their new addresses.
+
+---
+
+### 6. (Optional) Keep the old domain as an alias
+
+To ensure incoming mail for the old domain is still accepted:
+
+```bash
+docker compose exec admin flask mailu domain alias cymais.cloud infinito.nexus
+```
+
+This maps all `@cymais.cloud` addresses to their equivalents under `@infinito.nexus`.
+
+---
+
+## 💡 Summary
+
+* Do **not** just rename mailbox folders.
+* Always create the new domain and user in Mailu first.
+* Copy existing Maildir contents into the new user’s directory.
+* Remove Dovecot indices and fix permissions.
+* Optionally configure a **domain alias** so old addresses remain valid.