fix(examples): z80-led-chaser-c set the Z80 stack pointer in main

SDCC's z80 crt0 defaults SP to 0x0000; on the z80-cpu chip's memory map
(RAM 0x8000-0xBFFF, MMIO at 0xC000+) the stack would grow into unmapped
high memory and the program crashed on the first CALL (delay), so the LEDs
never moved. Set SP to the top of RAM (0xBFFF) at the start of main, the
same thing the asm Larson example does with "LD SP, 0xBFFF". Verified the
ROM runs and walks the LEDs.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

frontend/src/data/examples-retro-intel.ts

@@ -57,6 +57,15 @@ static void delay(unsigned int loops) {
 }
 
 void main(void) {
+    /* Park the stack at the top of the chip's 16 KB RAM (0x8000-0xBFFF).
+       SDCC's crt0 defaults SP to 0x0000; on this chip's memory map (RAM
+       0x8000-0xBFFF, MMIO at 0xC000+) that would push the stack onto
+       unmapped high memory and crash on the first CALL. The asm Larson
+       example does the same with "LD SP, 0xBFFF". */
+    __asm
+        ld sp, #0xBFFF
+    __endasm;
+
     unsigned char bit = 0x01;
     char dir = 1;          /* +1 = walking left, -1 = walking right */
     while (1) {