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/i18n/locales/en/files.json

@@ -1,4 +1,5 @@
 {
+  "linkedGone": "The file in the address is no longer in this list",
   "navLabel": "Files",
   "searchPlaceholder": "Search files…",
   "count_one": "{{count}} item",

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

@@ -1,5 +1,6 @@
 {
   "loading": "Loading…",
+  "linkedFailed": "The video in the address could not be opened",
   "backToOriginal": "Back to the original video",
   "back": "Back",
   "previous": "Previous",

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

@@ -1,4 +1,5 @@
 {
+  "linkedGone": "A címben szereplő fájl már nincs ebben a listában",
   "navLabel": "Fájlok",
   "searchPlaceholder": "Keresés a fájlok között…",
   "count_one": "{{count}} elem",

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

@@ -1,5 +1,6 @@
 {
   "loading": "Betöltés…",
+  "linkedFailed": "A címben szereplő videó nem nyitható meg",
   "backToOriginal": "Vissza az eredeti videóhoz",
   "back": "Vissza",
   "previous": "Előző",