ai tags: add buttons for quickly adding and removing tags on the /ai_tags page.

Add "Add" and "Remove" buttons beneath thumbnails on the /ai_tags page.
These let you add the tag to the post if it's correct, or remove it if
it's wrong.

app/controllers/ai_tags_controller.rb

@@ -12,4 +12,26 @@ class AITagsController < ApplicationController
 
     respond_with(@ai_tags)
   end
+
+  # Add the tag to the post, or remove the tag from the post.
+  def tag
+    @ai_tag = authorize AITag.find_by!(media_asset_id: params[:media_asset_id], tag_id: params[:tag_id])
+    @post = @ai_tag.post
+
+    if params[:mode] == "remove"
+      @post.remove_tag(@ai_tag.tag.name)
+      flash.now[:notice] = DText.format_text("Post ##{@post.id}: Removed [[#{@ai_tag.tag.pretty_name}]].", inline: true).html_safe
+    else
+      @post.add_tag(@ai_tag.tag.name)
+      flash.now[:notice] = DText.format_text("Post ##{@post.id}: Added [[#{@ai_tag.tag.pretty_name}]].", inline: true).html_safe
+    end
+
+    @post.save
+    if @post.invalid?
+      flash.now[:notice] = DText.format_text("Couldn't update post ##{@post.id}: #{@post.errors.full_messages.join("; ")}", inline: true).html_safe
+    end
+
+    @preview_size = params[:size].presence || cookies[:post_preview_size].presence || PostGalleryComponent::DEFAULT_SIZE
+    respond_with(@ai_tag)
+  end
 end