Fix followed games: send the query document instead of a rotating persisted hash

[einanderson]

"Following - Games" is empty: the route raises NotFound because Twitch answers the request with
PersistedQueryNotFound.

Cause

helix/games.py::_get_followed sends a persisted query with a hard-coded sha256Hash
(8446d4d2…). Twitch rotates those hashes, so the stored one eventually stops resolving and
the endpoint returns nothing usable.

The change

Send the full query document instead of the persisted hash:

query FollowingGames_CurrentUser($limit: Int!, $type: FollowedGamesType!) {
  currentUser { followedGames(first: $limit, type: $type) {
    nodes { id name displayName boxArtURL viewersCount } } } }

The batch form (a list) is kept, so the response shape is identical
([0].data.currentUser.followedGames.nodes) and nothing changes on the add-on side —
routes/followed.py and the converter are untouched.

Verification

Reproduced directly against gql.twitch.tv (persisted hash → PersistedQueryNotFound, full
document → the nodes), and confirmed in Kodi 21.3 on two boxes: the folder lists the followed
games again.

Note: the query still filters on type: LIVE, unchanged from before. A test without the filter
returned the same set here, so it is not the cause of an empty folder.

The follow/unfollow mutations in the same file still use persisted hashes. They are a different
matter — Twitch answers those with IntegrityCheckFailed for third-party clients regardless of
the hash, so replacing it there would not help.