feat(managers): table / cards / rows layouts for the channel manager (E4 S3)

A generic ViewSwitcher (reused from the feed) drives a per-account layout
shared by the Subscriptions + Discovery tabs. `table` keeps the DataTable
(numbered pager); `cards` and `rows` render a virtualized grid over the same
client-side list via the new ChannelLayoutGrid, which composes cells straight
from each table's Column<T> render closures (cardPrimary/hideInCard/cardLabel),
so both tabs — with their different columns — get the views for free. Status
chips surface in the fixed band when the table's own controls row is gone.

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

@@ -8,6 +8,12 @@
     "discovery": "Discover from playlists",
     "blocked": "Blocked"
   },
+  "layoutLabel": "Layout",
+  "layout": {
+    "table": "Table",
+    "cards": "Cards",
+    "rows": "Rows"
+  },
   "discovery": {
     "intro": "Channels that appear in your playlists but that you don't subscribe to. Subscribe to follow them — their new uploads will start showing in your feed (subscribing costs a little YouTube quota; existing videos aren't re-fetched).",
     "loading": "Finding channels…",

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

@@ -8,6 +8,12 @@
     "discovery": "Felfedezés a lejátszási listákból",
     "blocked": "Letiltott"
   },
+  "layoutLabel": "Nézet",
+  "layout": {
+    "table": "Táblázat",
+    "cards": "Kártya",
+    "rows": "Sor"
+  },
   "discovery": {
     "intro": "Csatornák, amelyek megjelennek a lejátszási listáidban, de még nem iratkoztál fel rájuk. Iratkozz fel, hogy kövesd őket — az új feltöltéseik megjelennek a hírfolyamodban (a feliratkozás kevés YouTube-kvótát használ; a meglévő videókat nem tölti le újra).",
     "loading": "Csatornák keresése…",