Minecraft2Shell

Support persistent working directory and Windows shell selection. ShellCommand: add getInitialWorkingDirectory, setWorkingDirectory and parseCommand to handle cd commands (including bare cd -> home), persist changes to config, and run cd without spawning a process. Use configured workingDirectory as ProcessBuilder.directory and honor a configurable windowsShell (cmd or powershell) when launching commands. Refactor saveCommandOutput to delegate to runCommandInternal. ModConfig: add workingDirectory and windowsShell fields. ModConfigScreen: add UI option to choose Windows shell.