feat(db): add M2 likes schema (general_likes, _albums, _artists)

Three tables keyed on (user_id, entity_id) with liked_at. Per-table
indexes on (user_id, liked_at DESC) for the recently-liked feed.
sqlc queries cover like/unlike/list-rows/count/list-ids per entity.

internal/db/queries/likes.sql

@@ -0,0 +1,62 @@
+-- name: LikeTrack :exec
+INSERT INTO general_likes (user_id, track_id)
+VALUES ($1, $2)
+ON CONFLICT (user_id, track_id) DO NOTHING;
+
+-- name: UnlikeTrack :exec
+DELETE FROM general_likes WHERE user_id = $1 AND track_id = $2;
+
+-- name: ListLikedTrackRows :many
+SELECT t.* FROM tracks t
+JOIN general_likes l ON l.track_id = t.id
+WHERE l.user_id = $1
+ORDER BY l.liked_at DESC
+LIMIT $2 OFFSET $3;
+
+-- name: CountLikedTracks :one
+SELECT count(*) FROM general_likes WHERE user_id = $1;
+
+-- name: ListLikedTrackIDs :many
+SELECT track_id FROM general_likes WHERE user_id = $1 ORDER BY liked_at DESC;
+
+-- name: LikeAlbum :exec
+INSERT INTO general_likes_albums (user_id, album_id)
+VALUES ($1, $2)
+ON CONFLICT (user_id, album_id) DO NOTHING;
+
+-- name: UnlikeAlbum :exec
+DELETE FROM general_likes_albums WHERE user_id = $1 AND album_id = $2;
+
+-- name: ListLikedAlbumRows :many
+SELECT a.* FROM albums a
+JOIN general_likes_albums l ON l.album_id = a.id
+WHERE l.user_id = $1
+ORDER BY l.liked_at DESC
+LIMIT $2 OFFSET $3;
+
+-- name: CountLikedAlbums :one
+SELECT count(*) FROM general_likes_albums WHERE user_id = $1;
+
+-- name: ListLikedAlbumIDs :many
+SELECT album_id FROM general_likes_albums WHERE user_id = $1 ORDER BY liked_at DESC;
+
+-- name: LikeArtist :exec
+INSERT INTO general_likes_artists (user_id, artist_id)
+VALUES ($1, $2)
+ON CONFLICT (user_id, artist_id) DO NOTHING;
+
+-- name: UnlikeArtist :exec
+DELETE FROM general_likes_artists WHERE user_id = $1 AND artist_id = $2;
+
+-- name: ListLikedArtistRows :many
+SELECT a.* FROM artists a
+JOIN general_likes_artists l ON l.artist_id = a.id
+WHERE l.user_id = $1
+ORDER BY l.liked_at DESC
+LIMIT $2 OFFSET $3;
+
+-- name: CountLikedArtists :one
+SELECT count(*) FROM general_likes_artists WHERE user_id = $1;
+
+-- name: ListLikedArtistIDs :many
+SELECT artist_id FROM general_likes_artists WHERE user_id = $1 ORDER BY liked_at DESC;