feat(db): add similarity lookup queries (ListActiveContextualLikesForUser, GetCurrentSessionVectorForUser)

internal/db/queries/contextual_likes.sql

@@ -8,3 +8,14 @@ VALUES ($1, $2, $3, $4);
 UPDATE contextual_likes
 SET deleted_at = now()
 WHERE user_id = $1 AND track_id = $2 AND deleted_at IS NULL;
+
+-- name: ListActiveContextualLikesForUser :many
+-- Returns all the user's active (non-soft-deleted) contextual_likes with
+-- non-null vectors. Cardinality is bounded by the user's actual like-while-
+-- playing history — typically tens to low hundreds. Used by the engine to
+-- compute contextual_match_score for the candidate pool.
+SELECT track_id, session_vector
+FROM contextual_likes
+WHERE user_id = $1
+  AND deleted_at IS NULL
+  AND session_vector IS NOT NULL;