fix: make audio actually play (four flecs systems were dead: with: [])

Same with: [] (zero-term) trap as the drag-and-drop fix, but it silently
killed four runtime systems -- so audio loaded but never played and the
clock stayed at 0:00:

- Update   (ON_UPDATE): never called Rl.update_music_stream, so miniaudio
  never pumped its buffers -> no sound, get_music_time_played stayed 0.
- Input    (PRE_UPDATE): keyboard controls (space, seek keys, M) dead.
- ApplySeek(PRE_UPDATE): seeking dead.
- Study    (ON_UPDATE): study-mode auto-pause FSM dead.

A zero-term system never iterates its block in this flecs build. Gave each
a real term (with: [playback_state]) so they match the player entity and
run every frame. The play/smart-play buttons already called audio.resume
via RmlUi -- they just had no stream pumping behind them.

Verified end-to-end (synthetic Xdnd drop + ARGV load): file loads ->
plays -> current_time advances 0..duration -> end-of-track auto-pause.

1 files changed, 4 insertions, 4 deletions

diff --git a/game/study_player/study_player.rb b/game/study_player/study_player.rb
index 8b6997b..c9f0508 100644
--- a/game/study_player/study_player.rb
+++ b/game/study_player/study_player.rb
@@ -487,7 +487,7 @@ module StudyPlayer
     SEEK_PCT_STEP = 0.10  # 10%: J / L
 
     def self.build_system(world, player_entity, runtime, playback_state, study_state)
-      world.system("Input", with: [], phase: Flecs::PRE_UPDATE) do
+      world.system("Input", with: [playback_state], phase: Flecs::PRE_UPDATE) do
         pb = player_entity.get(playback_state)
         next unless pb
 
@@ -685,7 +685,7 @@ end
 module StudyPlayer
   class UpdateSystem
     def self.build(world, player_entity, runtime, playback_state)
-      world.system("Update", with: [], phase: Flecs::ON_UPDATE) do
+      world.system("Update", with: [playback_state], phase: Flecs::ON_UPDATE) do
         pb = player_entity.get(playback_state)
         next unless pb && pb[:loaded]
 
@@ -732,7 +732,7 @@ module StudyPlayer
     SKIP_FRAMES = 3
 
     def self.build(world, player_entity, runtime, playback_state)
-      world.system("ApplySeek", with: [], phase: Flecs::PRE_UPDATE) do
+      world.system("ApplySeek", with: [playback_state], phase: Flecs::PRE_UPDATE) do
         pb = player_entity.get(playback_state)
         next unless pb && pb[:loaded] && pb[:seek_pending]
 
@@ -768,7 +768,7 @@ end
 module StudyPlayer
   class StudySystem
     def self.build(world, player_entity, runtime, playback_state, study_state)
-      world.system("Study", with: [], phase: Flecs::ON_UPDATE) do
+      world.system("Study", with: [playback_state], phase: Flecs::ON_UPDATE) do
         pb = player_entity.get(playback_state)
         ss = player_entity.get(study_state)
         next unless pb && ss && pb[:loaded]