feat: Smooth Snake game rendering and expand kernel subsystems

- Implement flicker-free atomic double-buffered frame rendering and sub-tick input polling in userland/lazybox/snake.c
- Add multi-input support (PS/2 keyboard scancodes and serial ANSI arrow escape sequences)
- Add sound effects (food beep, game over chime) and live speed scaling (+/- keys, P to pause)
- Add POSIX /dev/shm shared memory subsystem in ipc/shm_posix.c and include/ipc/shm_posix.h
- Add DNS resolver cache with TTL tracking in net/ipv4/dns_cache.c and include/net/dns_cache.h
- Add audio tone and jingle synthesizer in sound/beep.c and include/sound/beep.h
- Add %o octal formatting support in lib/vsprintf.c
- Add LazyBox applets: 'shm', 'dnscache', and 'beep'

include/sound/beep.h

@@ -0,0 +1,11 @@
+#ifndef _SOUND_BEEP_H
+#define _SOUND_BEEP_H
+
+#include <stdint.h>
+#include <stddef.h>
+
+void sound_play_tone(uint32_t freq_hz, uint32_t duration_ms);
+void sound_play_jingle(const char* jingle_name);
+int applet_beep(int argc, char** argv);
+
+#endif // _SOUND_BEEP_H