docs(cli): add Windows child-process guidance

[JJasonSun]

Summary

• add Windows Node integration guidance for the libuv teardown assertion associated with mixing synchronous discovery and live asynchronous child-process handles
• document multiline argument corruption when CALL-E is launched through cmd /c
• provide a shell-free spawn(process.execPath, argv) example that resolves the published CLI entry point, preserves multiline goals as one argument, and waits for process closure
• link the CLI installation guide to the Windows child-process troubleshooting section
• include a documentation-only empty changeset

Validation

• pnpm test
• pnpm check
• pnpm pack:dry-run
• git diff --check
• shell-free call plan --help launch on macOS with Node 26

Closes CALLE-AI/awesome-phone-call-agents#177

Related to CALLE-AI/awesome-phone-call-agents#159