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/__tests__/polyfill-dialog.ts

@@ -0,0 +1,16 @@
+/**
+ * jsdom doesn't implement HTMLDialogElement.showModal/close.
+ * Call this in beforeAll() for tests that render <Dialog>.
+ */
+export function polyfillDialog(): void {
+	if (typeof HTMLDialogElement.prototype.showModal !== "function") {
+		HTMLDialogElement.prototype.showModal = function showModal() {
+			this.setAttribute("open", "");
+		};
+	}
+	if (typeof HTMLDialogElement.prototype.close !== "function") {
+		HTMLDialogElement.prototype.close = function close() {
+			this.removeAttribute("open");
+		};
+	}
+}