feat: implement basic fairy tracker

app/controllers/fairy_controller.rb

@@ -0,0 +1,34 @@
+class FairyController < ApplicationController
+  def mark
+    instance_id, location = mark_params
+    instance = Instance.find_by(public_id: instance_id)
+    fairy = Fairy.new(location: location, instance_id: instance.id)
+    unless params[:pwd]
+      fairy.is_suggested = true
+    end
+
+    if fairy.save
+      new_instance = Instance.includes(:fairies).find(instance.id)
+      render partial: "instance/fairies", locals: { instance: new_instance }
+    end
+  end
+
+  def unmark
+    instance_id, location = mark_params
+    if params[:pwd]
+      instance = Instance.find_by(public_id: instance_id)
+      Fairy.delete_by(instance_id: instance.id, location: location)
+      new_instance = Instance.includes(:fairies).find(instance.id)
+      render partial: "instance/fairies", locals: { instance: new_instance }
+    end
+  end
+
+  def despawn
+  end
+
+  private
+
+  def mark_params
+    params.expect(:instance, :location)
+  end
+end