fix(qbzd): use SetState.next_track for auto-advance + periodic state reports

When iOS controls via QConnect without sending a queue, the local
QbzCore queue is empty so auto-advance fails. Now we extract next_track
from each SetState command, store it in DaemonCore, and the orchestrator
uses it as a fallback when the local queue is empty.

Also adds a periodic state reporter (every 2s) so iOS knows the
renderer's actual state (playing/paused/stopped + position). Without
this iOS thinks the daemon is still playing after a track ends.

Bump version to 0.1.9.

cc

crates/qbzd/Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "qbzd"
-version = "0.1.8"
+version = "0.1.9"
 edition.workspace = true
 license.workspace = true
 description = "QBZ headless music daemon for SBCs and servers"