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/lib/plexUrlState.dom.test.ts

@@ -48,15 +48,26 @@ const BASE: PlexUrlState = {
 };
 
 describe("plexParamUpdates", () => {
-  it("emits nothing for the all-default state", () => {
+  it("writes the default view in full: this account remembers one a link must not inherit", () => {
     expect(plexParamUpdates(BASE)).toEqual({
-      pscope: null,
-      psort: null,
-      pshow: null,
-      pf: null,
+      pscope: "both",
+      psort: "title:asc",
+      pshow: "all",
+      pf: "",
     });
   });
 
+  it("a link to the default view opens it over another remembered one", () => {
+    const params = applyUpdates(plexParamUpdates(BASE));
+    const back = plexParamsToState(params, {
+      scope: "movie",
+      sort: { key: "year", dir: "desc" },
+      show: "watched",
+      filters: RICH_FILTERS,
+    });
+    expect(back).toEqual(BASE);
+  });
+
   it("clears every key when passed null (off-plex page)", () => {
     expect(plexParamUpdates(null)).toEqual({
       pscope: null,
@@ -66,7 +77,7 @@ describe("plexParamUpdates", () => {
     });
   });
 
-  it("emits only non-default keys", () => {
+  it("writes the view picked", () => {
     const u = plexParamUpdates({
       scope: "movie",
       sort: { key: "year", dir: "desc" },
@@ -76,7 +87,7 @@ describe("plexParamUpdates", () => {
     expect(u.pscope).toBe("movie");
     expect(u.psort).toBe("year:desc");
     expect(u.pshow).toBe("in_progress");
-    expect(u.pf).toBeNull();
+    expect(u.pf).toBe("");
   });
 });