Fix oxlint warnings, extract dialog polyfill, deny warnings in gate

Adds void to floating promise in bestiary-cache.ts, extracts shared
polyfillDialog() helper to eliminate unbound-method warnings in 3 test
files. Adds --deny warnings to oxlint so future warnings fail the
build.

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

apps/web/src/components/__tests__/create-player-modal.test.tsx

@@ -4,19 +4,11 @@ import { playerCharacterId } from "@initiative/domain";
 import { cleanup, render, screen } from "@testing-library/react";
 import { userEvent } from "@testing-library/user-event";
 import { afterEach, beforeAll, describe, expect, it, vi } from "vitest";
+import { polyfillDialog } from "../../__tests__/polyfill-dialog.js";
 import { CreatePlayerModal } from "../create-player-modal.js";
 
 beforeAll(() => {
-	HTMLDialogElement.prototype.showModal =
-		HTMLDialogElement.prototype.showModal ||
-		function showModal(this: HTMLDialogElement) {
-			this.setAttribute("open", "");
-		};
-	HTMLDialogElement.prototype.close =
-		HTMLDialogElement.prototype.close ||
-		function close(this: HTMLDialogElement) {
-			this.removeAttribute("open");
-		};
+	polyfillDialog();
 });
 
 afterEach(cleanup);