dsh-mcu-lab: Closed-Loop 51 Microcontroller Development

`dsh-mcu-lab` is a DSH plugin designed to automate the microcontroller development (compilation, simulation, and evaluation) workflow. It provides 5 tools (such as `mcu_run`) and a command-line kernel at the plugin layer, supports Keil C51 and SDCC, and integrates Proteus simulation for deterministic evaluation. Installation requires placing the repository into the DSH profile directory and configuring environment variables. The plugin depends on Windows, Python, and Keil/Proteus, addressing the pain point of unstable traditional manual evaluation and enabling a closed-loop AI development process.