lock safesearch preference when level is moderate or strict

SearXNG's preferences.lock list prevents users from changing a setting
via the UI — it greys out the option. Without this, safe_search in
settings.yml was only a server default that users could still override
in their preferences page.

For moderate/strict, add:
  preferences:
    lock:
      - safesearch

For none, the lock is omitted so users can freely adjust it.

https://claude.ai/code/session_012gDnantBmFTWZGCiKyjazx

configure-searxng-safesearch.sh

@@ -190,6 +190,10 @@ set -u
   printf 'general:\n  instance_name: "Local Search"\n'
   printf 'server:\n  secret_key: "%s"\n  limiter: false\n' "$SECRET_KEY"
   printf 'search:\n  safe_search: %d\n  default_lang: "en"\n  formats: [html, json]\n' "$SAFE_INT"
+  # Lock the safe-search preference so users cannot override it via the UI
+  if [[ "$LEVEL" != "none" ]]; then
+    printf 'preferences:\n  lock:\n    - safesearch\n'
+  fi
   if [[ -n "$ENGINE_BLOCK" ]]; then
     printf 'engines:\n'
     printf '%b' "$ENGINE_BLOCK"