Add tests for undo/redo/setTempHp use cases, fix coverage thresholds

Adds missing tests for undoUseCase, redoUseCase, and setTempHpUseCase,
bringing application layer coverage from ~81% to 97%. Removes
autoUpdate from coverage thresholds and sets floors to actual values
so they enforce a real minimum.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

packages/application/src/__tests__/helpers.ts

@@ -1,6 +1,14 @@
-import type { Encounter, PlayerCharacter } from "@initiative/domain";
-import { isDomainError } from "@initiative/domain";
-import type { EncounterStore, PlayerCharacterStore } from "../ports.js";
+import type {
+	Encounter,
+	PlayerCharacter,
+	UndoRedoState,
+} from "@initiative/domain";
+import { EMPTY_UNDO_REDO_STATE, isDomainError } from "@initiative/domain";
+import type {
+	EncounterStore,
+	PlayerCharacterStore,
+	UndoRedoStore,
+} from "../ports.js";
 
 export function requireSaved<T>(value: T | null): T {
 	if (value === null) throw new Error("Expected store.saved to be non-null");
@@ -52,3 +60,17 @@ export function stubPlayerCharacterStore(
 	};
 	return stub;
 }
+
+export function stubUndoRedoStore(
+	initial: UndoRedoState = EMPTY_UNDO_REDO_STATE,
+): UndoRedoStore & { saved: UndoRedoState | null } {
+	const stub = {
+		saved: null as UndoRedoState | null,
+		get: () => initial,
+		save: (state: UndoRedoState) => {
+			stub.saved = state;
+			stub.get = () => state;
+		},
+	};
+	return stub;
+}