Stop the first play of each sound paying for its own load

Reported from the game: sounds sometimes start a bit late. The samples were
the suspect, so they were measured first - and they are clean. True digital
silence at the head of each file:

  seven of nine start on sample 1
  sfx_gas_blast    0.2ms
  sfx_black_hole   1.5ms, then a deliberate swell

The black hole's slow attack is the sound it was written to be - make_sfx.py
says it "swells across most of its length instead of decaying from the first
sample" - so there is nothing to trim without breaking it.

The delay was in the playback path, and "sometimes" was the clue:

  play() called load() every time. A cache hit after the first, but the
  FIRST play of each sound was a synchronous read and decode on the frame
  the sound was asked for. Ten sounds, ten occasional late starts.

  _pool() built its twelve AudioStreamPlayer nodes lazily, on the first
  play() call - one bigger stall, every session.

The catalog is preloaded now, so play() never touches the disk, and
Sfx.warm() builds the voices next to Music.ensure() at startup.

Case F pins the thing that was originally suspected, since make_sfx.py
regenerates these and a lazy envelope would hide the delay somewhere nobody
would look. It reads the source .wav's RIFF chunks rather than the imported
stream: these import as QOA (compress/mode=2), so AudioStreamWAV.data is not
PCM. The first version of that check was vacuous for exactly that reason and
passed at a 0.5ms threshold; it now reports "9 samples checked, worst attack
sfx_black_hole.wav at 1.5ms" and fails when tightened.

Not touched: project.godot has no [audio] section, so output_latency is at
its default. On Android that buffer is usually the dominant latency, but
lowering it risks crackle on real hardware - worth doing with someone
listening, not blind.

172/172.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_019AJMdB7iuHuLFZM1aBu3GD

ui/MainMenu.gd

@@ -56,6 +56,9 @@ func _ready() -> void:
 	# #148: the theme starts here, at the first screen, and keeps playing
 	# through every scene after it.
 	Music.ensure(get_tree())
+	# Same moment, same reason: build the sfx voices before the first
+	# sound needs them rather than during it.
+	Sfx.warm(get_tree())
 	play_button.pressed.connect(_on_play_pressed)
 	editor_button.pressed.connect(_on_editor_pressed)
 	editor_button.enabled = true