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/channelsUrlState.ts

@@ -2,10 +2,11 @@
 // from the address bar so a manager view is bookmarkable/shareable — the analogue of the feed's
 // urlState and Plex's plexUrlState. Keys are NAMESPACED (`ctab`/`csort`/`cf`) so they're
 // channels-unique (like `?v=`/`?pl`/`pscope`): no other provider ever reads or clears them, and the
-// feed's URL-stripping can't delete them out from under the manager. Only non-default values are
-// emitted, so URLs stay clean. The name search (`cq`) is part of the view like the rest: a bookmark of a
-// searched list opens searched.
-import { decodeSortParam, encodeSortParam, type SortState } from "./columnSort";
+// feed's URL-stripping can't delete them out from under the manager. The tab, sort and filters are
+// always written, their defaults too: a page opened without them takes this browser's remembered view,
+// which may not be the one bookmarked. The name search (`cq`) is part of the view like the rest (a
+// bookmark of a searched list opens searched), but nothing remembers it, so only a term is written.
+import { decodeSortParamOrNone, encodeSortParamOrNone, type SortState } from "./columnSort";
 import { type FilterMap } from "./tableColumns";
 import { decodeFilterMap, encodeFilterMap } from "./filterMapParam";
 
@@ -23,12 +24,11 @@ export const CHANNELS_KEYS = ["ctab", "csort", "cf", "cq"] as const;
 const KEYS = CHANNELS_KEYS;
 const VIEWS = ["subscribed", "discovery", "hidden", "blocked"];
 
-// Sort ⇄ `key:dir` (e.g. `subscribers:desc`) via the shared codec in columnSort. There is no default
-// sort here (fallback null), so any sort emits — no default short-circuit needed. The filter map rides
-// as one JSON value (lib/filterMapParam).
+// Sort ⇄ `key:dir` (e.g. `subscribers:desc`, `none` unsorted) via the shared codec in columnSort. The
+// filter map rides as one JSON value (lib/filterMapParam), an empty one as `cf=`.
 
 /** The address-bar delta for the manager content state: each namespaced key mapped to its emitted
- * value, or null to delete it (so a control back at its default clears the key). Pass `null` to clear
+ * value, or null to delete it (only the search's, when cleared). Pass `null` to clear
  * ALL manager keys — used when the app is off the Channels page (localStorage still holds the state; it
  * re-mirrors on return). Feed the result into urlWithParams(). */
 export function channelsParamUpdates(
@@ -36,9 +36,9 @@ export function channelsParamUpdates(
 ): Record<string, string | null> {
   if (!state) return { ctab: null, csort: null, cf: null, cq: null };
   return {
-    ctab: state.view && state.view !== "subscribed" ? state.view : null,
-    csort: encodeSortParam(state.sort),
-    cf: encodeFilterMap(state.filters),
+    ctab: state.view || "subscribed",
+    csort: encodeSortParamOrNone(state.sort),
+    cf: encodeFilterMap(state.filters) ?? "",
     cq: state.search.trim() || null,
   };
 }
@@ -55,10 +55,10 @@ export function channelsParamsToState(
   base: ChannelsUrlState,
 ): ChannelsUrlState {
   const tab = params.get("ctab");
-  const csort = params.get("csort");
+  const linkedSort = decodeSortParamOrNone(params.get("csort"));
   return {
     view: tab && VIEWS.includes(tab) ? tab : base.view,
-    sort: csort != null ? (decodeSortParam(csort) ?? base.sort) : base.sort,
+    sort: linkedSort === undefined ? base.sort : linkedSort,
     filters: params.has("cf") ? decodeFilterMap(params.get("cf") ?? "") : base.filters,
     search: params.get("cq") ?? base.search,
   };