Keep Windows qtx.exe consistent with quantex.exe across self-upgrade and uninstall

[Drswith]

Summary

Track the behavior gap called out in Discussion #69 for Windows standalone installs.

Today install.ps1 installs quantex.exe and then copies it to qtx.exe, but the binary self-upgrade path operates on the currently executing executable path and does not explicitly define or test dual-file replacement semantics.

Source

• Discussion [Decision] qtx 作为推荐入口与免安装试用在 README 的呈现 #69: [Decision] qtx 作为推荐入口与免安装试用在 README 的呈现 #69

Why this needs its own issue

This affects observable install and self-upgrade behavior, so it should land through a dedicated OpenSpec change in the self-upgrade domain rather than being bundled into the README documentation work.

Expected outcomes

• define the intended Windows aliasing model
• make self-upgrade and uninstall behavior consistent with that model
• add tests and docs/runbook coverage for the chosen behavior