feat(music): stable queue identity, remove/reorder, and repeat commands

TrackEntry gets a QueueID generated once when a track is queued and
kept for its whole life there, and musicrepo.ReplaceQueue now upserts
by that ID instead of deleting and reinserting the whole queue on
every sync (which churned every track's database id constantly, even
ones that hadn't moved, and would've made remove/reorder commands
target the wrong track). RemoveFromQueue and Reorder are new Manager
functions built on top of that stable identity. Also adds repeat_song/
repeat_queue to the persisted now-playing state, and makes the two
existing toggle functions actually sync it, they never did before.

schema.sql

@@ -150,7 +150,9 @@ CREATE TABLE IF NOT EXISTS music_now_playing (
     duration_seconds INT NOT NULL,
     started_at TIMESTAMPTZ NOT NULL,
     paused BOOLEAN NOT NULL DEFAULT FALSE,
-    volume INT NOT NULL DEFAULT 100
+    volume INT NOT NULL DEFAULT 100,
+    repeat_song BOOLEAN NOT NULL DEFAULT FALSE,
+    repeat_queue BOOLEAN NOT NULL DEFAULT FALSE
 );
 
 CREATE TABLE IF NOT EXISTS music_queue (
@@ -160,13 +162,15 @@ CREATE TABLE IF NOT EXISTS music_queue (
     track_title TEXT NOT NULL,
     track_url TEXT NOT NULL,
     requested_by BIGINT NOT NULL,
-    added_at TIMESTAMPTZ DEFAULT NOW()
+    added_at TIMESTAMPTZ DEFAULT NOW(),
+    client_id UUID NOT NULL DEFAULT gen_random_uuid(),
+    UNIQUE (guild_id, client_id)
 );
 
 CREATE TABLE IF NOT EXISTS music_commands (
     id BIGSERIAL PRIMARY KEY,
     guild_id BIGINT NOT NULL,
-    command_type TEXT NOT NULL CHECK (command_type IN ('skip', 'pause', 'resume', 'set_volume', 'remove_track', 'reorder')),
+    command_type TEXT NOT NULL CHECK (command_type IN ('skip', 'pause', 'resume', 'set_volume', 'remove_track', 'reorder', 'repeat_song', 'repeat_queue')),
     payload JSONB,
     requested_by BIGINT NOT NULL,
     created_at TIMESTAMPTZ DEFAULT NOW(),