state: persist the queue and pick up where playback stopped

The queue, its shuffle order and whether playback was running are written to
~/.local/state/rsplayer/state.json whenever they change, and on shutdown, then
restored at daemon start. Tracks that disappeared from disk are dropped
instead of failing on play.

`rsp resume`/`rsp toggle` now start the restored track when nothing is loaded
into the engine yet, which is the state right after a restart with a queue
that was paused.

1 files changed, 3 insertions, 1 deletions

diff --git a/TODO.md b/TODO.md
index 55f7d52..291a4f4 100644
--- a/TODO.md
+++ b/TODO.md
@@ -1,6 +1,8 @@
 # TODO
 
-- **Persist queue state** - Save queue to disk so it survives daemon restarts.
+- [x] **Persist queue state** - Queue, shuffle order and play state are written to `~/.local/state/rsplayer/state.json` and restored on start; `rsp resume` picks up a session that was paused when the daemon stopped
+
+- **Resume mid-track** - Store the playback offset with the queue state and seek there on restore (needs `rsp seek`)
 
 - [x] **Dynamic autocompletion of artists, albums and tracks** - `rsp complete <entity> [prefix]` queries DB directly; zsh completion wrapper concatenated via install.sh