On Windows, the daemon stop command was failing with "exit status 1" because
`taskkill` without `/F` flag does not work for console processes that do not
have windows to receive close messages.
Changes:
- Use `os.Process.Kill()` which calls Windows `TerminateProcess` API
- This is the reliable way to terminate processes on Windows
- The graceful RPC shutdown is already attempted before falling back to kill
- Updated error messages to be platform-agnostic (removed SIGTERM/SIGKILL)
The fix uses Go cross-platform process APIs instead of shelling out to
external commands, which is more reliable and portable.
Closes#992
Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
