test: warning=failure guard + fix ambiguous switch selector

- setupTests.js: console.error/warn now throw. Warning = failure.
- Combat.characterization: two role=switch (player HP + NPC HP), scope
  to player-HP label. getByRole('switch') was ambiguous.

Full suite: 77/77 pass, 0 warnings.

src/setupTests.js

@@ -1,5 +1,6 @@
 // jest setup: RTL jest-dom + mock DB reset per test.
 import '@testing-library/jest-dom';
+import { resetMockDb } from './__mocks__/firebase/_mock-db';
 
 // RTL v14: tell React this is an act environment. Without it every
 // async update warns "current testing environment is not configured to
@@ -21,11 +22,6 @@ console.warn = (...args) => {
   originalWarn(...args);
   throw new Error(`console.warn in test: ${args.map(String).join(' ').slice(0, 500)}`);
 };
-import { resetMockDb } from './__mocks__/firebase/_mock-db';
-
-// Tell React this is an act environment. Without it, every act() call
-// emits 'current testing environment is not configured to support act'.
-globalThis.IS_REACT_ACT_ENVIRONMENT = true;
 
 // polyfill crypto.randomUUID for jsdom (used by generateId in App.js).
 if (!global.crypto) global.crypto = {};

src/tests/Combat.characterization.test.js

@@ -123,7 +123,9 @@ describe('Combat -> Firebase', () => {
   test('toggleHidePlayerHp: updateDoc patch on activeDisplay/status', async () => {
     await setupWithMonsters();
     await startCombatViaUI();
-    const switchBtn = screen.getByRole('switch');
+    // Two switches now (Hide player HP + Hide NPC/monster HP). Scope to player one.
+    const playerHpLabel = screen.getByText('Hide player HP');
+    const switchBtn = playerHpLabel.parentElement.querySelector('[role="switch"]');
     fireEvent.click(switchBtn);
     await waitFor(() => {
       const adCalls = findCallActiveDisplay('updateDoc');