feat: add Captain::Scenario Model and API [CW-4597] (#11907)

Co-authored-by: Muhsin Keloth <muhsinkeramam@gmail.com>

db/migrate/20250710145708_create_captain_scenarios.rb

@@ -0,0 +1,18 @@
+class CreateCaptainScenarios < ActiveRecord::Migration[7.1]
+  def change
+    create_table :captain_scenarios do |t|
+      t.string :title
+      t.text :description
+      t.text :instruction
+      t.jsonb :tools, default: []
+      t.boolean :enabled, default: true, null: false
+      t.references :assistant, null: false
+      t.references :account, null: false
+
+      t.timestamps
+    end
+
+    add_index :captain_scenarios, :enabled
+    add_index :captain_scenarios, [:assistant_id, :enabled]
+  end
+end