fix(player+lidarr): mini-player sync race; durable approve + dedup

player: setQueueFromTracks fast-starts a single source at player-index 0
while the full queue is broadcast, so the transient currentIndexStream→0
emission clobbered the correct mediaItem with queue.value[0] (the first
track). Mini bar / playlist marker pinned to the wrong track until a
later index event (~the "passive ~30s recovery"). Track a logical-index
base so the player→queue mapping stays correct during the fill window;
also fixes the latent forward-fill auto-advance off-by-base.

lidarr #50: approving no longer fails when Lidarr is down. Approve
records the decision durably first, then best-effort adds; the
reconciler idempotently (re)sends unconfirmed adds every tick until they
stick (new additive lidarr_add_confirmed_at; AddArtist/AddAlbum map
Lidarr's "already exists" 400 → ErrAlreadyExists). No failed-state or
expiry by design — Lidarr keeps trying, operator monitors.

lidarr #51: Create() is now idempotent — a non-terminal request for the
same MBID returns the existing row instead of inserting a duplicate.

Rewrites the obsolete LidarrUnreachable_503 test to assert the durable-
approve contract; threads a client factory into NewReconciler.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

internal/lidarr/errors.go

@@ -14,6 +14,12 @@ var (
 	ErrLookupFailed   = errors.New("lidarr: lookup failed") // 4xx other than 401/403
 	ErrServerError    = errors.New("lidarr: server error")  // 5xx
 	ErrInvalidPayload = errors.New("lidarr: invalid payload")
+	// ErrAlreadyExists is returned by AddArtist/AddAlbum when Lidarr
+	// rejects the add with a 400 because the artist/album is already in
+	// its library. This is the desired end state, not a failure — the
+	// idempotent retry path (reconciler re-sending an add after a partial
+	// success) treats it as confirmed rather than spinning forever.
+	ErrAlreadyExists = errors.New("lidarr: already exists")
 	// ErrNotFound is returned by LookupArtistByMBID and LookupAlbumByMBID
 	// when Lidarr returns 200 with an empty array — i.e., the MBID isn't in
 	// Lidarr's monitored set. Distinguished from network/auth errors so admin