Add ability to hide posts from unregistered users.

templates/editor.html

@@ -8,6 +8,7 @@
   <div class="two-col"><label>Category<input name="category" value="{{ post.category if post else 'Engineering' }}" placeholder="Engineering"></label><label>Summary<input name="excerpt" required value="{{ post.excerpt if post else '' }}" placeholder="The one-paragraph signal"></label></div>
   <label>Article<textarea name="body" required rows="16" placeholder="Write in plain text. Paragraph breaks are preserved.">{{ post.body if post else '' }}</textarea><small>Wrap code in triple backticks. Add a language after the opening backticks, for example <code>```python</code>.</small></label>
   <label>Article image<input name="image" type="file" accept="image/jpeg,image/png,image/webp">{% if post and post.image_filename %}<small>Leave empty to retain the current image.</small>{% endif %}</label>
+  <label class="post-visibility"><input name="is_hidden" type="checkbox" value="1" {% if post and post.is_hidden %}checked{% endif %}> Members only <small>Hide this post from visitors who are not signed in.</small></label>
   <fieldset class="step-images"><legend>Step images</legend><p>Upload images for individual repair steps, then place <code>[[image:1]]</code>, <code>[[image:2]]</code>, and so on in the article text.</p><div id="step-image-list"><div class="step-image-row"><label>Image<input name="images" type="file" accept="image/jpeg,image/png,image/webp"></label><label>Caption<input name="image_captions" type="text" placeholder="Optional caption"></label></div></div><button class="add-step-image" type="button">Add another step image</button></fieldset>
   <button class="button" type="submit">Publish transmission <span aria-hidden="true">→</span></button>
 </form>