Fix permission denied when --force overwrites root-owned config files

When Docker containers write config files (e.g. searxng/settings.yml),
those files end up owned by root. write_if_new now falls back to
sudo tee when the destination file exists but is not writable.

https://claude.ai/code/session_012gDnantBmFTWZGCiKyjazx

laptop_full_setup.sh

@@ -535,7 +535,11 @@ write_if_new() {
     local dest="$1"
     local content; content=$(cat)
     if [[ ! -f "$dest" ]] || $FORCE; then
-        printf '%s\n' "$content" > "$dest"
+        if [[ -e "$dest" ]] && [[ ! -w "$dest" ]]; then
+            printf '%s\n' "$content" | sudo tee "$dest" > /dev/null
+        else
+            printf '%s\n' "$content" > "$dest"
+        fi
         ok "Wrote $(basename "$dest")"
     else
         info "Kept   $(basename "$dest")  (--force to overwrite)"