feat(decomp): main lane m55bbba — 1 banked

One clean whole-EXE rebuild verified the batch (gate_main), and main re-checked
BYTE-IDENTICAL against config/check.us.sha before anything was credited.

  func_8003D630

src/sgap_3.c

@@ -1,3 +1,7 @@
 #include "common.h"
 
-INCLUDE_ASM("asm/nonmatchings/sgap_3", func_8003D630);
+extern void SpuQuit(void);
+
+void func_8003D630(void) {
+    SpuQuit();
+}