Initial commit: C64 project skeleton with oscar64 submodule

src/helloworld.c

@@ -0,0 +1,23 @@
+// helloworld.c — minimal C64 program in C with Oscar64
+//
+// Builds a .prg that prints "Hello World" on the C64 text screen and exits.
+//
+// Build:  ../scripts/build.sh
+// Run:    x64 helloworld.prg   (or use ../scripts/build.sh -e to run in
+//                              the built-in oscar64 emulator)
+
+#include <stdio.h>
+
+int main(void)
+{
+	// CHR$(147) is PETSCII "clear screen" — same as printf("\f") in C but
+	// emitted as the right byte for the C64's PETSCII character set.
+	putchar(147);
+
+	// The p"" prefix tells Oscar64 to emit the string as PETSCII, not ASCII.
+	// Without it the C64's character ROM would render garbage because the
+	// character generator maps 'H' to PETSCII 8, not ASCII 72.
+	printf(p"Hello World\n");
+
+	return 0;
+}