Bump audio command FIFO size for SDL 3 callback cadence

The audio engine queues sound-control commands (PATCH, PAN, PLAY,
STOP, etc.) into an sfifo for the audio thread to consume from inside
_run_commands(). The FIFO was sized at 128 commands, which was fine
under SDL 1.2's push-callback model: the driver fired callbacks at a
predictable cadence that drained the FIFO promptly.

SDL 3's pull-stream model on macOS calls our audio callback ~25-30 ms
apart with 4096-byte (1024-sample) chunks. Under sustained
multi-channel activity (e.g. holding fire in Classic mode, where
xkobo_shot generates several commands per shot at ~33 Hz), the FIFO
fills faster than the audio thread drains it and overflows. Each
overflowed command is a silently dropped sound event — audibly
manifest as unevenly-spaced shot sounds.

Bumping to 1024 gives the FIFO plenty of headroom (the drain rate at
~250 Hz handles thousands of commands/sec; the FIFO only needs to
absorb burst arrivals between drain ticks).

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

sound/a_commands.h

@@ -28,7 +28,15 @@
 extern "C" {
 #endif
 
-#define	MAX_COMMANDS	128
+/*
+ * SDL 3 migration: the audio command FIFO was sized 128 for the SDL 1.2
+ * push-callback model where the driver fired predictably-spaced
+ * callbacks that drained the FIFO promptly. SDL 3's pull-stream model
+ * can call the audio callback less often / with larger buffers, so
+ * commands accumulate between drains. 1024 gives a comfortable
+ * headroom even under sustained heavy fire.
+ */
+#define	MAX_COMMANDS	1024
 
 /*----------------------------------------------------------
 	Asynchronous command interface stuff