本地工具路径DTU_*环境变量改造落地：10处调用点去硬编码+变量优先解析，本机全链路验证通过，文档同步收口，requirements补pre-commit

MDK-ARM/reset.bat

@@ -1,11 +1,38 @@
 @echo off
 setlocal
 
-set STLINK=C:\Program Files (x86)\STMicroelectronics\STM32 ST-LINK Utility\ST-LINK Utility\ST-LINK_CLI.exe
-if not exist "%STLINK%" (
-    echo RESET_FAIL: ST-LINK_CLI not found at "%STLINK%"
-    exit /b 2
+:: ST-LINK CLI location: env var DTU_STLINK_CLI = full path of ST-LINK_CLI.exe.
+:: Explicit value is used as-is (invalid value = hard error, no silent fallback);
+:: when unset, fall back to PATH (where ST-LINK_CLI.exe).
+set "STLINK="
+if defined DTU_STLINK_CLI goto stlink_check
+where ST-LINK_CLI.exe >nul 2>&1
+if errorlevel 1 goto stlink_missing
+for /f "delims=" %%i in ('where ST-LINK_CLI.exe 2^>nul') do (
+    if not defined STLINK set "STLINK=%%i"
 )
+if not defined STLINK goto stlink_missing
+goto stlink_done
+
+:stlink_check
+if exist "%DTU_STLINK_CLI%" goto stlink_done
+echo ENV_ERROR: DTU_STLINK_CLI is set but does not exist: "%DTU_STLINK_CLI%"
+echo Fix the variable value. No fallback to PATH or other installs is attempted.
+exit /b 2
+
+:stlink_missing
+echo ENV_ERROR: ST-LINK_CLI.exe not found (DTU_STLINK_CLI unset and not on PATH)
+echo Set it to the full path of ST-LINK_CLI.exe, e.g.:
+echo   [Environment]::SetEnvironmentVariable('DTU_STLINK_CLI', 'C:\Tools\STLink\ST-LINK_CLI.exe', 'User')
+exit /b 2
+
+:stlink_done
+if not defined STLINK set "STLINK=%DTU_STLINK_CLI%"
+if exist "%STLINK%" goto stlink_ready
+echo RESET_FAIL: ST-LINK_CLI not found at "%STLINK%"
+exit /b 2
+
+:stlink_ready
 
 if "%~1"=="" goto :reset_run
 if /i "%~1"=="hard" goto :hard