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'

sound/beep.c

@@ -0,0 +1,60 @@
+// Audio Beep & Tone Synthesizer for SUB-OS
+#include <sound/beep.h>
+#include <drivers/speaker.h>
+#include <arch/x86_64/pit.h>
+#include <lib/string.h>
+#include <lib/printf.h>
+#include <kernel/printk.h>
+
+void sound_play_tone(uint32_t freq_hz, uint32_t duration_ms) {
+    if (freq_hz == 0 || duration_ms == 0) return;
+    #if defined(__x86_64__)
+    speaker_beep(freq_hz, duration_ms);
+    #else
+    printk(ANSI_BRIGHT_MAGENTA "♪ [Tone %u Hz for %u ms]\n" ANSI_RESET, freq_hz, duration_ms);
+    #endif
+}
+
+void sound_play_jingle(const char* jingle_name) {
+    if (!jingle_name) return;
+
+    if (strcmp(jingle_name, "startup") == 0) {
+        sound_play_tone(523, 60); // C5
+        sound_play_tone(659, 60); // E5
+        sound_play_tone(784, 60); // G5
+        sound_play_tone(1046, 120);// C6
+    } else if (strcmp(jingle_name, "coin") == 0) {
+        sound_play_tone(988, 40); // B5
+        sound_play_tone(1318, 100);// E6
+    } else if (strcmp(jingle_name, "alert") == 0) {
+        sound_play_tone(880, 80);
+        sound_play_tone(440, 80);
+    } else {
+        sound_play_tone(440, 100);
+    }
+}
+
+int applet_beep(int argc, char** argv) {
+    uint32_t freq = 440;
+    uint32_t dur = 100;
+
+    if (argc >= 2) {
+        if (strcmp(argv[1], "startup") == 0 || strcmp(argv[1], "coin") == 0 || strcmp(argv[1], "alert") == 0) {
+            printk(ANSI_BRIGHT_CYAN "Playing jingle '%s'...\n" ANSI_RESET, argv[1]);
+            sound_play_jingle(argv[1]);
+            return 0;
+        }
+        freq = (uint32_t)strtol(argv[1], NULL, 10);
+    }
+    if (argc >= 3) {
+        dur = (uint32_t)strtol(argv[2], NULL, 10);
+    }
+
+    if (freq < 20) freq = 20;
+    if (freq > 20000) freq = 20000;
+    if (dur > 5000) dur = 5000;
+
+    printk(ANSI_BRIGHT_CYAN "Beeping at %u Hz for %u ms...\n" ANSI_RESET, freq, dur);
+    sound_play_tone(freq, dur);
+    return 0;
+}