Add presence validation and update NPC entity creation logic in App.tsx

src/app/App.tsx

@@ -5668,10 +5668,38 @@ export function App({ store, initialStatusMessage }: AppProps) {
     try {
       const trimmedModelAssetId = npcModelAssetIdDraft.trim();
       const colliderMode = overrides.colliderMode ?? npcColliderModeDraft;
+      const presence =
+        npcPresenceModeDraft === "always"
+          ? createNpcAlwaysPresence()
+          : createNpcTimeWindowPresence({
+              startHour: normalizeTimeOfDayHours(
+                readFiniteNumberDraft(
+                  npcPresenceStartHourDraft,
+                  "NPC presence start hour"
+                )
+              ),
+              endHour: normalizeTimeOfDayHours(
+                readFiniteNumberDraft(
+                  npcPresenceEndHourDraft,
+                  "NPC presence end hour"
+                )
+              )
+            });
+
+      if (
+        presence.mode === "timeWindow" &&
+        presence.startHour === presence.endHour
+      ) {
+        throw new Error(
+          "NPC presence window start and end hours must differ."
+        );
+      }
+
       const nextEntity = createNpcEntity({
         id: selectedNpc.id,
         name: selectedNpc.name,
         actorId: npcActorIdDraft,
+        presence,
         position: snapVec3ToGrid(
           readVec3Draft(entityPositionDraft, "NPC position"),
           DEFAULT_GRID_SIZE