Implement measurements create/destroy and index listing

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

app/models/measurement.rb

@@ -1,3 +1,17 @@
 class Measurement
   include ActiveModel::Model
+
+  attr_accessor :readouts, :created_at
+
+  def id
+    created_at.to_i
+  end
+
+  def to_param
+    id.to_s
+  end
+
+  def persisted?
+    true
+  end
 end