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

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

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

@@ -0,0 +1,26 @@
+-- Cheap fingerprint (file names, sizes and modification times) used to skip
+-- content hashing of soundtracks that have not changed since the last sync.
+ALTER TABLE soundtrack ADD COLUMN fingerprint TEXT NOT NULL DEFAULT '';
+
+-- Play queues. Every client has its own queue, identified by the queue's UUID.
+-- Ended queues are kept as history.
+CREATE TABLE queue (
+    uuid UUID PRIMARY KEY DEFAULT gen_random_uuid(),
+    current_song INT4 NOT NULL DEFAULT -1,
+    -- The last random song, added to the queue by /music/addQue.
+    last_fetched_song_uuid UUID NULL,
+    started_at TIMESTAMPTZ NOT NULL DEFAULT NOW(),
+    ended_at TIMESTAMPTZ NULL
+);
+CREATE INDEX idx_queue_active ON queue(uuid) WHERE ended_at IS NULL;
+
+-- song_uuid has no foreign key: a sync can delete songs. The names are kept for the history.
+CREATE TABLE queue_song (
+    queue_uuid UUID NOT NULL REFERENCES queue(uuid) ON DELETE CASCADE,
+    song_no INT4 NOT NULL,
+    song_uuid UUID NOT NULL,
+    soundtrack_name VARCHAR NOT NULL,
+    song_name VARCHAR NOT NULL,
+    added_at TIMESTAMPTZ NOT NULL DEFAULT NOW(),
+    PRIMARY KEY (queue_uuid, song_no)
+);

internal/db/migrations/000006_add_soundtrack_fingerprint.up.sql

@@ -1,3 +0,0 @@
--- Cheap fingerprint (file names, sizes and modification times) used to skip
--- content hashing of soundtracks that have not changed since the last sync.
-ALTER TABLE soundtrack ADD COLUMN fingerprint TEXT NOT NULL DEFAULT '';