feat: Phase 1 网络端到端打通 + FirstInit/Login/DevMode 完善

- 用户态共享网络协议栈 CODE/tools/net_stack.h（eth/ARP/IPv4/ICMP/UDP-DNS/TCP static inline，轮询模型）
- shell 内建 ping/curl/run 命令；ping.elf/curl.elf 对齐 net_stack.h 真实协议栈
- shell dev_mode 串口镜像（g_serial_mirror）便于自动化验证
- DSK 启动流程：firstInit.txt 双行格式（firstInit + dev_mode），dev_mode=1 触发 shell 自动回归测试
- FirstInit 完成→持久化 USER.CONF + 翻转 firstInit 0->1（保留 dev_mode）
- firstInit=1 时 DSK 加载 login.elf 进行用户选择 + 密码校验后再进 desktop
- 新增 CODE/login/ 登录应用、CODE/DKM/dkm_shared.h、Logo.png
- ahci/e1000/virtio_net/fat32/console_fb 驱动更新；utsm serial/block/dsk_loader 调整
- build.ps1 打包 ping.elf/curl.elf 进 SATA FAT32 根目录
- 移除 CODE/tools/bash（与 shell.elf 重复）

CODE/UTSM/test/utsm_selftest.c

@@ -1,16 +1,25 @@
 #include <utsm/utsm.h>
 #include <utsm/log.h>
 #include <utsm/segment.h>
+#include <utsm/arena.h>
 
 int memcmp(const void *a, const void *b, usize len);
 usize strlen(const char *s);
 
 int utsm_selftest_run(void) {
-    utsm_process_context process;
-    utsm_process_create_test(&process, 1);
+    log_info("[UTSM] selftest enter");
+
+    /* utsm_process_context is ~8KB (256 capabilities × 32 bytes).
+     * Allocate from arena instead of stack to avoid kernel stack overflow. */
+    utsm_process_context *process = (utsm_process_context *)kmem_alloc(sizeof(utsm_process_context));
+    if (!process) {
+        log_error("[UTSM] selftest: failed to allocate process context");
+        return UTSM_ERR_NO_MEMORY;
+    }
+    utsm_process_create_test(process, 1);
 
     utsm_capability cap;
-    int status = utsm_create_segment(&process, UTSM_PAGE_SIZE, UTSM_SEG_F_READ | UTSM_SEG_F_WRITE | UTSM_SEG_F_STRONG_RECOVERY, &cap);
+    int status = utsm_create_segment(process, UTSM_PAGE_SIZE, UTSM_SEG_F_READ | UTSM_SEG_F_WRITE | UTSM_SEG_F_STRONG_RECOVERY, &cap);
     if (status != UTSM_OK) {
         log_error("[UTSM] selftest create segment failed");
         return status;