feat: Add Rust Base64 codec, Process hierarchy (pstree, kill), and VFS visual tree/find applets

- Implement memory-safe RFC-4648 Base64 encoder and decoder in rust/src/crypto/base64.rs
- Add process parent hierarchy tracking (ppid, pgid), task_find_by_pid, task_kill, and task_dump_pstree in kernel/task.c
- Add list_for_each_entry macro in include/lib/list.h
- Add LazyBox applets: 'base64', 'pstree', 'kill', 'tree', 'find', and 'traceroute'

include/lib/list.h

@@ -53,4 +53,9 @@ static inline int list_empty(const struct list_head *head) {
     for (pos = (head)->next, n = pos->next; pos != (head); \
         pos = n, n = pos->next)
 
+#define list_for_each_entry(pos, head, member) \
+    for (pos = list_entry((head)->next, typeof(*pos), member); \
+         &pos->member != (head); \
+         pos = list_entry(pos->member.next, typeof(*pos), member))
+
 #endif // _LIB_LIST_H