Drop EnableInMainMenu=true - broke Emby's modern ViewManager

Real error from the field: navigating to the party page threw inside
Emby's own viewmanager.js (v4.10.0.40): TypeError, cannot read
properties of undefined (reading lifeCycleAbortSignal), at
getResumeOptions/dispatchViewBeforeShow. EnableInMainMenu=true was
never confirmed by any real example (only EnableInUserMenu=true was,
via the forum thread cited in Plugin.cs) - it very likely routes the
page through the newer ViewManager meant for full content views
(Home, Movies, ...), which expects a lifecycle contract this static
embedded-resource page doesn't provide. Reverting to exactly the
confirmed-working combination.

The raw page itself was confirmed served correctly beforehand (200,
correct content, via GET /web/configurationpage?name=WatchPartyRoom)
so the plugin/registration side was never the problem - just this one
flag.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

src/WatchParty/Plugin.cs

@@ -63,7 +63,13 @@ namespace WatchParty
                 Name = "WatchPartyRoom",
                 DisplayName = "Watch Party",
                 EmbeddedResourcePath = GetType().Namespace + ".Configuration.partyPage.html",
-                EnableInMainMenu = true,
+                // EnableInMainMenu=true was a guess, not confirmed anywhere, and
+                // it broke: Emby's modern ViewManager (v4.10.x) crashed trying to
+                // route this page as a full nav "view" (TypeError reading
+                // 'lifeCycleAbortSignal' in viewmanager.js - see git history).
+                // The one real-world confirmed-working example only ever used
+                // EnableInUserMenu=true with EnableInMainMenu left false/default,
+                // so that's what this now matches exactly.
                 EnableInUserMenu = true,
                 MenuIcon = "group",
                 IsMainConfigPage = false