fix(VideoPlayer): work around slow Firefox MediaCapabilities.decodingInfo

Firefox's navigator.mediaCapabilities.decodingInfo costs ~14 ms per call
(out-of-process RDD decoder probe). Shaka Player calls it once per Variant
in the DASH manifest while filtering supported variants, and YouTube
manifests routinely have 1000+ variants, so player initialization stalls
15-20 s on Gecko-based browsers before the first SourceBuffer is added.

Wrap decodingInfo to delegate "supported" checks to
MediaSource.isTypeSupported (sub-ms on Firefox) with a per-MIME cache.
DRM probes and non-media-source queries fall through to native.
Wrapper is gated to Gecko UAs so Chromium and Safari are unaffected.

Refs: https://github.com/shaka-project/shaka-player/issues/4775

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/main.js

@@ -1,3 +1,4 @@
+import "@/utils/firefoxMediaCapabilitiesFix.js";
 import { createApp } from "vue";
 import router from "@/router/router.js";
 import App from "./App.vue";