Shared-vitals overlay on a canvas

The original's DxHud overlay: the player's row, then one per character heard
from, each a health bar over split stamina and mana bars with percentages,
and for the others an arrow toward them relative to where the player faces
plus the distance, fading from white to red as they get further. Ctrl shows
a frame and a close box; Ctrl+drag moves it and the spot is saved per
character. /mm vitalsharing overlay toggles it.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

src/OpenAC.MosswartMassacre/FeatureCatalog.cs

@@ -35,5 +35,6 @@ internal static class FeatureCatalog
         features.Add(sharing);
         session.AddConnectionListener(sharing);
         session.AddShareHandler(sharing);
+        features.Add(new Sharing.VitalSharingOverlay(context, sharing));
     }
 }