fix(nav): a linked player, file and search survive what the app does by itself (review round 2)

- Playlists: a link over a playlist the account does not hold plays alone; the rail's own
  fallback no longer counts as a pick that gives the player up.
- The linked opener opens or clears nothing once the address names another player, and stops
  looking (and fetching its row) once it settled.
- Files: a list the server's cap cut — the sorted or searched one too — keeps the link, with a
  notice of its own (EN/HU).
- History: an in-place view rewrite (search refine, count, channel to channel, sub-view)
  drops a reloaded entry's overlay marks (replaceView); a landing on a channel opened from a
  search keeps the search; the Feed press on a search opens the plain feed.
- Files/Playlists: an emptied search is written at once.
- Client log: plf/cf (column text filters) are typed keys; the shell has none of its own.
- Contract: writers outside lib/ take a literal or a lib/ function's result; every URL key is
  sorted typed or not; the writer regexes are held by a fixture; sub-views named; the bookmark
  net reads page tags.
- Feed defaults in one constant; one live-search queue helper; Scheduler writes through the
  Activity codec; notRun copy (EN/HU) names Forward and a plain "Search YouTube" button.

frontend/src/i18n/locales/en/feed.json

@@ -77,7 +77,7 @@
     "cleared_other": "Cleared {{count}} results",
     "showHint": "How many results to fetch at a time — “Load more” pulls another batch of this size.",
     "notRunTitle": "Not searched yet",
-    "notRunBody": "A YouTube API search spends 100 units of the shared daily quota, so a reload, a link or Back doesn't start one by itself.",
-    "runAgain": "Search YouTube again"
+    "notRunBody": "A YouTube API search spends 100 units of the shared daily quota, so a reload, a link, Back or Forward doesn't start one by itself.",
+    "runAgain": "Search YouTube"
   }
 }

frontend/src/i18n/locales/en/files.json

@@ -1,5 +1,6 @@
 {
   "linkedGone": "The file in the address is no longer in this list",
+  "linkedNotListed": "The file in the link isn't among the files listed here — it may be further down the list",
   "navLabel": "Files",
   "searchPlaceholder": "Search files…",
   "count_one": "{{count}} item",

frontend/src/i18n/locales/hu/feed.json

@@ -77,7 +77,7 @@
     "cleared_other": "{{count}} találat törölve",
     "showHint": "Hány találatot szerezzen egyszerre — a „Továbbiak betöltése” ennyivel tölt tovább.",
     "notRunTitle": "Ez a keresés még nem futott le",
-    "notRunBody": "Egy YouTube API-keresés 100 egységet fogyaszt a közös napi kvótából, ezért újratöltéskor, linkről vagy visszalépéskor nem indul el magától.",
-    "runAgain": "Keresés újra a YouTube-on"
+    "notRunBody": "Egy YouTube API-keresés 100 egységet fogyaszt a közös napi kvótából, ezért újratöltéskor, linkről, vissza- vagy előrelépéskor nem indul el magától.",
+    "runAgain": "Keresés a YouTube-on"
   }
 }

frontend/src/i18n/locales/hu/files.json

@@ -1,5 +1,6 @@
 {
   "linkedGone": "A linkben szereplő fájl már nincs ebben a listában",
+  "linkedNotListed": "A linkben szereplő fájl nincs a listázottak között — lehet, hogy lejjebb van",
   "navLabel": "Fájlok",
   "searchPlaceholder": "Keresés a fájlok között…",
   "count_one": "{{count}} elem",