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'

ipc/shm_posix.c

@@ -0,0 +1,102 @@
+// POSIX Shared Memory Subsystem (/dev/shm) for SUB-OS
+// Implements shm_open, ftruncate, and shm_unlink functionality
+
+#include <ipc/shm_posix.h>
+#include <mm/kmalloc.h>
+#include <lib/string.h>
+#include <kernel/printk.h>
+
+static posix_shm_object_t shm_table[POSIX_SHM_MAX_OBJECTS];
+
+void posix_shm_init(void) {
+    memset(shm_table, 0, sizeof(shm_table));
+    // Create standard system shared memory segments
+    posix_shm_open("/subos_system_metrics", 0x40 | 0x02, 0666);
+    posix_shm_truncate(0, 4096);
+    posix_shm_open("/wayland_display_shm", 0x40 | 0x02, 0666);
+    posix_shm_truncate(1, 65536);
+
+    printk(KERN_INFO "SHM: POSIX /dev/shm Shared Memory subsystem initialized\n");
+}
+
+int posix_shm_open(const char* name, int flags, uint32_t mode) {
+    if (!name || name[0] != '/') return -1;
+
+    // Check if exists
+    for (int i = 0; i < POSIX_SHM_MAX_OBJECTS; i++) {
+        if (shm_table[i].active && strcmp(shm_table[i].name, name) == 0) {
+            shm_table[i].ref_count++;
+            return i;
+        }
+    }
+
+    // Create new
+    for (int i = 0; i < POSIX_SHM_MAX_OBJECTS; i++) {
+        if (!shm_table[i].active) {
+            strncpy(shm_table[i].name, name, POSIX_SHM_MAX_NAME - 1);
+            shm_table[i].name[POSIX_SHM_MAX_NAME - 1] = '\0';
+            shm_table[i].memory = NULL;
+            shm_table[i].size = 0;
+            shm_table[i].mode = mode ? mode : 0644;
+            shm_table[i].ref_count = 1;
+            shm_table[i].active = true;
+            return i;
+        }
+    }
+    return -1;
+}
+
+int posix_shm_truncate(int fd, size_t size) {
+    if (fd < 0 || fd >= POSIX_SHM_MAX_OBJECTS || !shm_table[fd].active) return -1;
+
+    if (shm_table[fd].memory) {
+        kfree(shm_table[fd].memory);
+    }
+
+    shm_table[fd].memory = kzalloc(size);
+    if (!shm_table[fd].memory && size > 0) {
+        shm_table[fd].size = 0;
+        return -1;
+    }
+    shm_table[fd].size = size;
+    return 0;
+}
+
+int posix_shm_unlink(const char* name) {
+    if (!name) return -1;
+    for (int i = 0; i < POSIX_SHM_MAX_OBJECTS; i++) {
+        if (shm_table[i].active && strcmp(shm_table[i].name, name) == 0) {
+            if (shm_table[i].memory) {
+                kfree(shm_table[i].memory);
+            }
+            memset(&shm_table[i], 0, sizeof(posix_shm_object_t));
+            return 0;
+        }
+    }
+    return -1;
+}
+
+posix_shm_object_t* posix_shm_get(int fd) {
+    if (fd < 0 || fd >= POSIX_SHM_MAX_OBJECTS || !shm_table[fd].active) return NULL;
+    return &shm_table[fd];
+}
+
+void posix_shm_dump(void) {
+    printk(ANSI_BRIGHT_CYAN "=== POSIX /dev/shm Shared Memory Registry ===\n" ANSI_RESET);
+    printk(ANSI_BOLD "%-4s  %-30s  %10s  %6s  %8s\n" ANSI_RESET, "FD", "NAME", "SIZE (B)", "PERMS", "NREF");
+    printk("-----------------------------------------------------------------\n");
+
+    int active_count = 0;
+    for (int i = 0; i < POSIX_SHM_MAX_OBJECTS; i++) {
+        if (shm_table[i].active) {
+            active_count++;
+            printk("%-4d  " ANSI_BRIGHT_YELLOW "%-30s" ANSI_RESET "  %10llu  0%03o   %8u\n",
+                   i, shm_table[i].name, (uint64_t)shm_table[i].size,
+                   shm_table[i].mode, shm_table[i].ref_count);
+        }
+    }
+    if (active_count == 0) {
+        printk("  (No active /dev/shm objects)\n");
+    }
+    printk("\n");
+}