feat(demo): demo scenarios and sample data tasks

Brings the T2 2026 demo work from ontrack-features-t2-2026 11.0.x (reviewed and merged work) onto thoth-tech 11.0.x.

Co-authored-by: maplefoxgit <s223932052@deakin.edu.au>
Co-authored-by: Ronit Khokhar <ronitkhokharr@gmail.com>
Co-authored-by: Gaurav Myana <s225108954@deakin.edu.au>

Author: 4 people

app/api/demo_scenario_api.rb

@@ -0,0 +1,22 @@
+# frozen_string_literal: true
+
+require 'grape'
+require Rails.root.join('lib/demo_data/all_features_scenario')
+
+class DemoScenarioApi < Grape::API
+  helpers AuthenticationHelpers
+
+  before do
+    header 'Cache-Control', 'private, no-store'
+    authenticated?
+  end
+
+  desc 'Get the guarded local mobile-feedback demo scenario contract',
+       tags: ['demo'],
+       summary: 'Get guarded local demo scenario'
+  get '/demo/scenario' do
+    DemoData::AllFeaturesScenario.contract_for(user: current_user)
+  rescue DemoData::AllFeaturesScenario::SafetyError
+    error!({ error: 'Not found.' }, 404)
+  end
+end