feat(player): the YouTube player and the file viewer are named in the address

The player names what it plays in its own history entry (watch, wrel, wtab): a reload or a
bookmark reopens it on the page that hosts it, with that page's list as the queue, or alone
from the catalog (GET /api/videos/{id}/row); a page that hosts none gets the shell's. Back
lands on the page's address without it (useBackToClose's url; ui/Modal passes it on). The
Files viewer and player do the same (fview, fplay). The Plex and channel-manager views are
always written in full, as their fallback is remembered state.

frontend/src/moduleUrl.contract.test.ts

@@ -16,6 +16,7 @@ import { plexParamUpdates, plexSearchParamUpdates } from "./lib/plexUrlState";
 import { activityParamUpdates, DEFAULT_ACTIVITY_STATE } from "./lib/activityUrlState";
 import { DEFAULT_LOGS_STATE, logsParamUpdates } from "./lib/logsUrlState";
 import { FILES_KEYS } from "./lib/filesUrlState";
+import { PLAYER_KEYS, playerParamUpdates } from "./lib/playerUrlState";
 import { playlistViewParamUpdates } from "./lib/playlistsUrlState";
 import { SETTINGS_TAB_KEY } from "./lib/settingsTab";
 import { CONFIG_TAB_KEY } from "./lib/configTab";
@@ -128,6 +129,14 @@ describe("module URL keys", () => {
     );
   });
 
+  // The player opens over any page too, and names itself in its own history entry.
+  it("leave the player's keys to the shell", () => {
+    const shell: readonly string[] = SHELL_KEYS;
+    expect(PLAYER_KEYS.filter((k) => !shell.includes(k))).toEqual([]);
+    const written = playerParamUpdates({ watch: "v1", related: "v2", panel: "related" });
+    expect(Object.keys(written).sort()).toEqual([...PLAYER_KEYS].sort());
+  });
+
   it.each([...REGISTERED_PAGES])("are exactly what %s's encoders write", (page) => {
     const declared = [...moduleDef(page).urlKeys].sort();
     const writes = WRITES[page];