feat(backup): deploy cron-based SQLite backups to production

- Create deploy/xamxam-backup.cron with hourly (30d) and daily (90d) jobs
- Add just recipes for deploying backup infrastructure:
  - deploy-backup-script: upload backup-sqlite.sh to /usr/local/bin
  - deploy-backup-cron: install cron.d file, create /var/backups/xamxam + log
  - deploy-backup: one-shot convenience (script + cron)
  - deploy-check-backup-log: tail the backup log
  - deploy-list-backups: ls remote backup directory
  - trigger-backup: manually invoke backup on server
  - test-restore: scp, gunzip, verify a remote snapshot
- Add reminder to run deploy-backup after first deploy
- Replace 'Contenu (Markdown)' label with 'Syntax Markdown' link (cheatsheet)

app/public/admin/form-help-inline-fragment.php

@@ -157,9 +157,10 @@ function renderEditor(Database $db, string $key): void
             </div>
 
             <label for="fhb-ed-<?= htmlspecialchars($key) ?>" class="fhb-edit-label">Contenu (Markdown) :</label>
+            <label for="fhb-ed-<?= htmlspecialchars($key) ?>" class="fhb-edit-label"><a href="https://herman.bearblog.dev/markdown-cheatsheet/" target="_blank">Syntax Markdown</a></label>
             <input type="hidden" id="fhb-content-<?= htmlspecialchars($key) ?>" name="content"
                    value="<?= htmlspecialchars($content) ?>">
-            <div id="fhb-editor-<?= htmlspecialchars($key) ?>" class="fhb-overtype-editor"></div>
+            <div id="fhb-editor-<?= htmlspecialchars($key) ?>" class="fhb-overtype-editor" style="height: 40vh !important; border: 1px dashed grey"></div>
 
             <div class="fhb-edit-buttons">
                 <button type="submit" class="btn btn--primary btn--sm">Enregistrer</button>