fix(notifications): a confirm names its user and channel again; t() and a notice's text are kept apart by a contract

The value sweep wrapped two plain t() values in raw(), so the delete-user and the YouTube subscribe
confirms read "[object Object]" where the email or the channel was. tsc cannot see that seam, so a
syntax contract now refuses a notice value handed to t() and an already-said text kept in a notice.
The raw() doc says what it is: text kept as fetched (a Plex title in the language it was fetched in).
seasonTitleText's no-number branches are tested.

frontend/src/features/plexCards/plexCards.lang.dom.test.tsx

@@ -74,6 +74,8 @@ describe("a season's name", () => {
     ["Season 1", 1, "plex.seasonTitle(1)"],
     ["Specials", 0, "plex.specials"],
     ["Book One: Water", 1, "Book One: Water"],
+    ["Season 4", null, "Season 4"],
+    ["", null, "plex.playlist.seasonUnknown"],
   ])("Plex's %j (season %s) reads %j", (title, n, shown) => {
     render(<SeasonCard se={season(title, n)} onOpen={vi.fn()} />);
     expect(screen.getByText(shown)).toBeTruthy();