fix(i18n): every counted string is a plural pair, so one reads singular

"1 seasons", "Synced 1 subscriptions", "1 video(s) were skipped": 21 English
strings carried {{count}} in one plain key and read plural at one. Each is a
_one/_other pair now (Hungarian keeps one form for both), and so is every other
counted string, so the next wording change is a plural too. A contract test
holds the rule for every locale file.

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

@@ -147,7 +147,8 @@
     "resetHint": "Wipe the demo account's playlists, hidden/watched/saved videos and settings, then re-seed a few sample playlists.",
     "resetTitle": "Reset demo state?",
     "resetConfirm": "This clears everything the demo account has accumulated — playlists, hidden/watched/saved videos and settings — and re-seeds a few sample playlists. It can't be undone.",
-    "resetDone": "Demo reset — {{count}} sample playlist(s) seeded",
+    "resetDone_one": "Demo reset — {{count}} sample playlist seeded",
+    "resetDone_other": "Demo reset — {{count}} sample playlists seeded",
     "resetFailed": "Couldn't reset the demo account",
     "removed": "Removed from the demo whitelist",
     "removeTitle": "Remove demo access?",
@@ -158,7 +159,8 @@
     "noPending": "No pending requests.",
     "addPlaceholder": "Add an email directly…",
     "add": "Add",
-    "decided": "{{count}} decided",
+    "decided_one": "{{count}} decided",
+    "decided_other": "{{count}} decided",
     "approved": "Approved {{email}} — they can sign in now",
     "approveFailed": "Couldn't approve the request",
     "denyFailed": "Couldn't deny the request",
@@ -243,7 +245,8 @@
     },
     "count_one": "{{count}} event · newest first",
     "count_other": "{{count}} events · newest first",
-    "capped": "showing the newest {{shown}} of {{count}}",
+    "capped_one": "showing the newest {{shown}} of {{count}}",
+    "capped_other": "showing the newest {{shown}} of {{count}}",
     "copy": "Copy",
     "copied_one": "Copied {{count}} event",
     "copied_other": "Copied {{count}} events",