Scenario action party.add

Lets a game without C# give the player a character from a scenario.

src/Actions/PartyAddAction.cs

@@ -0,0 +1,29 @@
+using Cthangover.Core.Actions;
+
+namespace Cthangover.Mods.Characters
+{
+    /// <summary>
+    /// <c>action party.add id=hero</c> — puts a character template into the
+    /// player's party and battle set. Lets a game without C# give the player
+    /// their starting party from its first scenario (a new game resets the
+    /// party and replays that scenario). A character already in the roster keeps
+    /// their level and health and only returns to the battle set.
+    /// </summary>
+    public class PartyAddAction : IScenarioAction
+    {
+        /// <summary>DSL name.</summary>
+        public string Name => "party.add";
+
+        /// <summary>Reads <c>id</c> and adds the character.</summary>
+        public void Run(IActionContext ctx)
+        {
+            var id = ctx.GetParam("id");
+            if (string.IsNullOrWhiteSpace(id))
+            {
+                ctx.LogWarning("EVENT", "party.add: missing 'id'");
+                return;
+            }
+            ctx.Character.AddToParty(id.Trim());
+        }
+    }
+}