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/ipc/shm_posix.h

@@ -0,0 +1,27 @@
+#ifndef _IPC_SHM_POSIX_H
+#define _IPC_SHM_POSIX_H
+
+#include <stdint.h>
+#include <stddef.h>
+#include <stdbool.h>
+
+#define POSIX_SHM_MAX_NAME 64
+#define POSIX_SHM_MAX_OBJECTS 32
+
+typedef struct {
+    char name[POSIX_SHM_MAX_NAME];
+    void* memory;
+    size_t size;
+    uint32_t mode;
+    uint32_t ref_count;
+    bool active;
+} posix_shm_object_t;
+
+void posix_shm_init(void);
+int posix_shm_open(const char* name, int flags, uint32_t mode);
+int posix_shm_truncate(int fd, size_t size);
+int posix_shm_unlink(const char* name);
+posix_shm_object_t* posix_shm_get(int fd);
+void posix_shm_dump(void);
+
+#endif // _IPC_SHM_POSIX_H