Store each client's play queue in the database

The queue lived in memory and was shared by all clients, so a restart or a
finished sync cleared it. Every client now has its own queue in the new
queue and queue_song tables (added to the undeployed migration 000006).

The music endpoints return the queue ID in the X-Queue-Id header and expect
it back. A request without an ID, or with an ended one, starts a new queue.
/music/reset ends the queue and returns a new ID, and a sync ends all
running queues. Ended queues are kept as history.

The deprecated legacy routes without the /api/v1 prefix are removed.

internal/db/migrations/000006_add_fingerprint_and_queue.down.sql

@@ -0,0 +1,3 @@
+DROP TABLE queue_song;
+DROP TABLE queue;
+ALTER TABLE soundtrack DROP COLUMN fingerprint;