fix(history): a sub-view reads only its own module's from the entry it mounts on

The entry's _sub now names its owner (_subOf, the module's address key). Signed out on a Plex season,
the sign-in card took the season for one of its modes and rendered a card with an empty button; the
other way round, Plex took the card's register view for one of its own. An entry an older build wrote
is read as the module's only when its address names one of that module's views.

frontend/src/modules/plex/PlexBrowse.playShow.dom.test.tsx

@@ -45,7 +45,7 @@ beforeAll(() => {
   globalThis.ResizeObserver ??= Stub as unknown as typeof ResizeObserver;
   globalThis.IntersectionObserver ??= Stub as unknown as typeof IntersectionObserver;
 });
-beforeEach(() => window.history.replaceState({ _sub: { kind: "grid" } }, ""));
+beforeEach(() => window.history.replaceState({ _sub: { kind: "grid" }, _subOf: "v" }, ""));
 afterEach(() => {
   cleanup();
   vi.restoreAllMocks();