Fix Redis persistence crash-loop and provisioning dependencies

- Disable Redis RDB snapshots (--save "") — Redis is cache-only for
  Nextcloud; snapshot writes failed due to directory permissions and
  blocked all Redis writes, causing background jobs to crash-loop at
  400%+ CPU
- Add passlib as a required local dependency (needed for password_hash
  filter in Ansible templates)
- Make dl role SFTP setup conditional on dl_sftp_authorized_keys being
  set in the vault
- Fix check-vault.sh stdin conflict (pipe + heredoc) by passing vault
  content via environment variable
- Remove dl_sftp_authorized_keys from required_scalars (it is optional)

scripts/check-vault.sh

@@ -24,10 +24,13 @@ fi
 echo "==> Decrypting vault (you will be prompted for the vault password)"
 VAULT_CONTENT=$(ansible-vault view "${VAULT_FILE}")
 
-echo "${VAULT_CONTENT}" | python3 - <<'PYEOF'
-import sys, yaml
+# Pass vault content via environment variable — avoids a pipe+heredoc stdin conflict
+# where python3 - consumes stdin for the script, leaving sys.stdin.read() empty.
+export VAULT_CONTENT
+python3 - <<'PYEOF'
+import os, sys, yaml
 
-data = yaml.safe_load(sys.stdin.read())
+data = yaml.safe_load(os.environ['VAULT_CONTENT'])
 
 # Required non-empty scalar strings
 required_scalars = [
@@ -41,7 +44,6 @@ required_scalars = [
     "roundcube_db_password",
     "roundcube_des_key",
     "vaultwarden_admin_token",
-    "dl_sftp_authorized_keys",
 ]
 
 # Required non-empty lists (must contain at least one entry)