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/columnSort.ts

@@ -53,6 +53,22 @@ export function decodeSortParam(raw: string): SortState {
   return parseSortState({ key, dir });
 }
 
+// The list's own order (no column sort) as a word of its own, for a page whose sort is remembered (an
+// account pref, this browser's view): there the sort is always written, because a page opened without
+// one takes the remembered sort, which may not be the one bookmarked.
+const UNSORTED = "none";
+
+export function encodeSortParamOrNone(s: SortState): string {
+  return encodeSortParam(s) ?? UNSORTED;
+}
+
+/** The sort an address names; `undefined` when it names none or a malformed one (the remembered one
+ * applies). */
+export function decodeSortParamOrNone(raw: string | null): SortState | undefined {
+  if (raw == null) return undefined;
+  return raw === UNSORTED ? null : (decodeSortParam(raw) ?? undefined);
+}
+
 /** The header-click cycle: unsorted → ascending → descending → unsorted. */
 export function cycleSort(current: SortState, key: string): SortState {
   if (!current || current.key !== key) return { key, dir: "asc" };