增加文件系统

.opencode/command/build.md

@@ -0,0 +1,14 @@
+---
+description: Build the STM32F4-Base Keil MDK project. Use ONLY when the user asks to build, compile, or verify the project.
+---
+
+Run the Keil MDK-ARM build from the project root:
+
+```
+cmd /c "cd /d "D:\Code\DTU 程序\STM32F4-Base\MDK-ARM" && build.bat"
+```
+
+Check the last 10 lines of `MDK-ARM/build_log.txt` for errors/warnings.
+Return code 0 = success (0 errors, 0 warnings).
+Return code 1 = warnings-only (also failure per project rules).
+Return code 2+ = compile errors.