feat: SKEL skeleton instrumentation - designed-but-unimplemented paths panic

- hypercall.c: 5 Phase 1.3 stubs -> HCALL-E01..E05 panic (no NOSYS return)
- drr_stub.c: snapshot alloc fail -> DRR-E01; new skeletons DRR-E02 root key
  seal, DRR-E03 task kill crypto erase, DRR-E04/E05 segment/system rollback,
  DRR-E06/E07 driver recovery ops dispatch
- sched.c: enable fail -> SCH-E02 panic (no silent demo skip)
- dkm/kernel_api.c: D1 hot-unload DKM-E01, D2 bare code loader DKM-E02,
  SIPI AP wake DKM-E03 skeletons
- virtio_net tx/rx stubs -> VNET-E01/E02; ath9k tx stub -> ATH-E01;
  xhci port reset -> XHC-E01; nvme MSI/MSI-X fail -> NVME-E01..E03 (no
  silent polling downgrade); e1000 MAC fallback -> E1K-E01
- pe_shim unimpl API -> PE-E01; PE ordinal import -> PE-E02
- kernel/main.c: lib sync / vscode install fail -> LNX-E01/E02
- NEW brand/brand.c (E1 boot anim BRAND-E01, E2 time egg BRAND-E02) and
  pkg/pkg.c (pacman skeleton PKG-E01..03), wired into UTSM MAKEFILE
- Deliberate design-internal fallbacks kept and documented (VMX skip,
  bzImage skip, KDE fallback, boot-module fallback, apic->PIC route)

CODE/UTSM/kernel/main.c

@@ -1,4 +1,5 @@
 #include <utsm/log.h>
+#include <utsm/panic.h>
 #include <utsm/arena.h>
 #include <utsm/utsm.h>
 #include <utsm/drr.h>
@@ -427,14 +428,22 @@ void kernel_main(void) {
                     if (g_compat_linux_lib_sync) {
                         int lsrc = lxc_sync_lib_dir(g_compat_linux_guest_path);
                         if (lsrc == 0) log_info("[UTSM] lib sync ok");
-                        else log_warn("[UTSM] lib sync skipped (non-fatal)");
+                        else {
+                            /* 严格错误策略插桩：lib 同步失败零降级（LNX-E01） */
+                            panic_full("LNX-E01 LIB SYNC FAILED",
+                                       "FAT32 lib dir sync to Linux guest failed", 0);
+                        }
                     }
                     /* VSCode Phase 5: tarball module 存在时装到 guest /opt/vscode
-                     * （已安装则秒跳过；失败不阻断启动，桌面降级显示未安装） */
+                     * （已安装则秒跳过；失败零降级 panic） */
                     if (g_compat_vscode_install) {
                         int vsrc = lxc_vscode_install();
                         if (vsrc == 0) log_info("[UTSM] vscode ready");
-                        else log_warn("[UTSM] vscode install skipped (non-fatal)");
+                        else {
+                            /* 严格错误策略插桩：VSCode 安装失败零降级（LNX-E02） */
+                            panic_full("LNX-E02 VSCODE INSTALL FAILED",
+                                       "vscode tarball install into guest failed", 0);
+                        }
                     }
                 } else {
                     log_error("[UTSM] Linux launch failed");