fix(nav): the address follows the view through overlays, reloads and Back (review round 1)

- A URL mirror names the view again on every entry Back or Forward lands on, so a change made
  under a dialog, a drawer or a sub-view is not undone by the next reload.
- A view pushed from the entry a reload under a dialog started from no longer inherits its overlay
  mark; a reload under two overlays closes onto the page in one step.
- The linked player reopens over a live search, gives itself up when its list moves first, and
  plays alone over an emptied playlist; a capped Files list keeps the link it cannot resolve.
- The Feed press over a channel ends the search; leaving a search ends its asked mark; Files and
  Playlists searches end with their page; the feed always names its view and debounces its search.
- Search-box keys are declared per module and kept out of the client log below TRACE.
- Writers outside lib/ go through codecs; the URL contract scans computed keys, overlay writers and
  two-line reads, and holds every page to a bookmark round trip (Config, Activity, Playlists and the
  Files sort and viewer added).

frontend/src/lib/settingsTab.ts

@@ -6,6 +6,11 @@ import { LS, setTabRaw } from "./storage";
 // address-bar key the page mirrors its tab to is here too, beside the other pages' keys.
 export const SETTINGS_TAB_KEY = "stab";
 
+/** The address-bar delta for the Settings tab shown. */
+export function settingsTabParams(tab: string | null): Record<string, string | null> {
+  return { [SETTINGS_TAB_KEY]: tab };
+}
+
 export type SettingsTabId =
   | "appearance"
   | "notifications"