Closes#1983
- Add scripts/installer/codewhale.nsi: NSIS installer that installs both
codewhale.exe and codewhale-tui.exe to %LOCALAPPDATA%\Programs\CodeWhale\bin,
adds to current-user PATH, and includes an uninstaller that cleans PATH
- Add docs/CLASSROOM_INSTALL.md: step-by-step checklist for IT admins
deploying CodeWhale in labs/classrooms, covering silent install, manual
fallback, API key provisioning, imaging notes, and troubleshooting
- Update docs/INSTALL.md: add Windows NSIS Installer section referencing
the new installer and classroom checklist
songzhenrui