P10.2: SFX bank over System Sound Services (sx / iOS)

Refactor GameAudio from the single clear cue into a full bank: load swap,
match, combo1..combo5, win, lose once at startup, each into its own
SystemSoundID via load_system_sound. Expose per-event play methods
(play_swap/play_match/play_cascade/play_win/play_lose), each a single
AudioServicesPlaySystemSound. play_cascade selects the ascending clip by
clamping cascade depth through the pure, OS-agnostic cascade_cue_index
(depth<=1 -> combo1, depth>=5 -> combo5) so P10.4 can snapshot it headlessly.

Layer stays purely additive and inline-if-OS==.ios guarded; the clear trigger
is migrated to sfx_cascade(mv.rounds.len) at its board_view call site, with
sfx_swap/match/win/lose shims staged for P10.3 wiring. No framework added
beyond the already-linked AudioToolbox/CoreFoundation (build.sx untouched).

main.sx

@@ -285,10 +285,10 @@ main :: () -> void {
     g_motion = xx context.allocator.alloc(size_of(GemMotion));
     g_motion.init();
 
-    // SFX (P8.1). Loads the one System Sound Services cue once; board_view
-    // plays it when a swap clears a match. Purely additive — never touches
-    // score/board/move state. On iOS the platform has already chdir'd to the
-    // bundle, so the cue's relative path resolves. No-op off iOS.
+    // SFX (P10.2). Loads the System Sound Services cue bank once; board_view
+    // plays a cue per event. Purely additive — never touches score/board/move
+    // state. On iOS the platform has already chdir'd to the bundle, so each
+    // cue's relative path resolves. No-op off iOS.
     g_audio = xx context.allocator.alloc(size_of(GameAudio));
     memset(xx g_audio, 0, size_of(GameAudio));
     g_audio.init();