Windows: official port -- UCRT static build, UTF-8 throughout, Low IL sandbox, ncurses TUI, installer; v0.6.0

Build
  * cross build switches to pkgsCross.ucrt64 (shell-win.nix); curl (Schannel),
    winpthreads and ncurses 6.6 are linked statically, so the release is
    cst-agent.exe + busybox.exe (busybox-w32 Unicode) with no extra DLLs
  * windres embeds a manifest with activeCodePage=UTF-8 and a version resource
  * ncurses 6.6 Windows console driver patches (mouse button state, A_DIM,
    wide-char declarations): scripts/patches/
  * scripts/bootstrap_msys2.sh builds the same release natively in MSYS2
    UCRT64; PR #1's MINGW64 notes now point there
  * vendor/tre-regex (musl's TRE) provides <regex.h> on MinGW

UTF-8
  * paths cross the system call boundary as UTF-16 (*W APIs); console code
    pages set to 65001 and restored on exit; files are read and written in
    binary mode
  * child output that is not valid UTF-8 is decoded from the console, OEM or
    ANSI system code page
  * read_file hides CR; edit_file, apply_patch and write_file keep CRLF line
    endings and a UTF-8 BOM

OS layer and processes
  * os_dir_* and cst_fnmatch replace the POSIX-only directory walks in
    subagent, plugins, skills, undo and fs_tools; realpath / path_under and
    symlink rejection work on Windows
  * every child goes through CreateProcessW with its own environment block
    inside a Job Object, so timeouts and Esc end the whole process tree

Sandbox (auto mode, "auto · lowil")
  * run_shell runs with a restricted Low integrity token; the workspace gets
    an inheritable Low label once, the sandbox TEMP is labeled Low, and the
    credentials file gets a no-read-up label
  * drive roots, the profile and system folders are never labeled
  * network commands still ask, since Low IL does not block the network;
    Access denied and MSYS2's 0xc0000142 offer a rerun outside the sandbox
  * /sandbox lists labeled folders, /sandbox reset-labels restores them

TUI
  * raster console fonts are switched to Consolas / NSimSun while running
  * the home logo falls back to text when the console font lacks U+2580
  * mouse drag copy goes to the Windows clipboard

Distribution
  * scripts/install_windows.ps1 installs a Gitea release into
    %LOCALAPPDATA%\Programs\cst-agent and adds it to the user PATH;
    cst-agent-update.cmd reruns it; scripts/release_windows.sh uploads the
    zip with the token taken from the environment
  * scripts/run_windows.bat is gone; docs/README-windows.md is rewritten

Tests
  * new test_lowil, test_win_utf8 and test_os_dir; tests made portable
    (cst_test_util.h)
  * scripts/win_test.sh and scripts/winvm/ run the suite on English and
    Chinese Windows Server VMs as Administrator, a standard user and a
    Chinese user name: 29/29 on all six

tests/test_config.c

@@ -9,6 +9,11 @@
 #include <string.h>
 #include <sys/stat.h>
 #include <unistd.h>
+#include "cst_test_util.h"
+#ifdef _WIN32
+#include <aclapi.h>
+#include <sddl.h>
+#endif
 
 #define CHECK(c)                                                               \
   do {                                                                         \
@@ -23,7 +28,7 @@ static char g_dir[256];
 static void write_file(const char *name, const char *text) {
   char path[512];
   snprintf(path, sizeof(path), "%s/cst-agent/%s", g_dir, name);
-  FILE *fp = fopen(path, "w");
+  FILE *fp = fopen(path, "wb");
   CHECK(fp);
   fputs(text, fp);
   fclose(fp);
@@ -57,9 +62,26 @@ static void test_creds(void) {
 
   char path[512];
   snprintf(path, sizeof(path), "%s/cst-agent/credentials", g_dir);
+#ifdef _WIN32
+  {
+    wchar_t *wp = os_utf8_to_wide(path);
+    PSECURITY_DESCRIPTOR sd = NULL;
+    LPWSTR s = NULL;
+    CHECK(wp && GetNamedSecurityInfoW(wp, SE_FILE_OBJECT,
+                                      LABEL_SECURITY_INFORMATION, NULL, NULL,
+                                      NULL, NULL, &sd) == ERROR_SUCCESS);
+    CHECK(ConvertSecurityDescriptorToStringSecurityDescriptorW(
+        sd, SDDL_REVISION_1, LABEL_SECURITY_INFORMATION, &s, NULL));
+    CHECK(wcsstr(s, L"NR") && wcsstr(s, L";ME)")); /* Low-IL cannot read */
+    LocalFree(s);
+    LocalFree(sd);
+    free(wp);
+  }
+#else
   struct stat st;
   CHECK(stat(path, &st) == 0);
   CHECK((st.st_mode & 0077) == 0);
+#endif
 
   CHECK(cst_creds_resolve("deepseek", key, sizeof(key), &from) == 0);
   CHECK(strcmp(from, "saved") == 0);
@@ -124,23 +146,20 @@ static void test_effort(void) {
 }
 
 int main(void) {
-  snprintf(g_dir, sizeof(g_dir), "/tmp/cst-config-XXXXXX");
-  CHECK(mkdtemp(g_dir));
+  CHECK(test_tmpdir(g_dir, sizeof(g_dir), "cst-config") == 0);
   setenv("XDG_CONFIG_HOME", g_dir, 1);
   unsetenv("DEEPSEEK_API_KEY");
   unsetenv("MINIMAX_API_KEY");
   unsetenv("OPENAI_API_KEY");
   char sub[300];
   snprintf(sub, sizeof(sub), "%s/cst-agent", g_dir);
-  CHECK(mkdir(sub, 0700) == 0);
+  CHECK(test_mkdir(sub, 0755) == 0);
 
   test_creds();
   test_settings();
   test_effort();
 
-  char cmd[400];
-  snprintf(cmd, sizeof(cmd), "rm -rf '%s'", g_dir);
-  CHECK(system(cmd) == 0);
+  CHECK(test_rmrf(g_dir) == 0);
   printf("test_config: OK\n");
   return 0;
 }