Improve first-run guidance

[hubertdungen]

Summary

• refuse unreliable attachment to an already-running X4 session
• show persistent Windows error dialogs for missing files and launch failures
• make the full-ZIP extraction and launch order prominent in the README and Reddit guide
• prepare the v0.2.1-beta package, version metadata, release notes, and CI artifact

Validation

• packaged locally with pinned Zig 0.16.0
• release smoke tests passed for 0.2.1-beta
• launcher built-in self-tests passed
• ZIP SHA-256 sidecar matches the generated archive
• launcher and hook product versions both report 0.2.1-beta

User-visible fix

Users must close X4 and run X4TripleScreen.exe; the launcher starts the game itself and loads the hook before X4 creates its Vulkan window. Steam may remain open.