Fix CMake 3.12 compatibility by adding required install destinations

[Copilot]

The install(TARGETS ...) command in cmake/ftxui_install.cmake was missing required destination specifications that became mandatory in CMake 3.12+. This caused build failures when users tried to install FTXUI with the minimum supported CMake version.

The issue occurred because the install command:

install(
  TARGETS screen dom component
  EXPORT ftxui-targets
  )

Was missing explicit destination specifications for different artifact types. CMake 3.12+ requires these destinations to be explicitly declared.

This PR adds the required destination specifications:

install(
  TARGETS screen dom component
  EXPORT ftxui-targets
  ARCHIVE DESTINATION "${CMAKE_INSTALL_LIBDIR}"
  LIBRARY DESTINATION "${CMAKE_INSTALL_LIBDIR}"
  RUNTIME DESTINATION "${CMAKE_INSTALL_BINDIR}"
  )

The fix ensures that:

• Static libraries (.a files) are installed to the archive destination
• Shared libraries are installed to the library destination
• Executables are installed to the runtime destination

All destinations use CMake's standard directory variables for proper cross-platform compatibility. The change is backward compatible and maintains the same installation behavior while satisfying CMake 3.12+ requirements.

Fixes #1118.

---

💬 Share your feedback on Copilot coding agent for the chance to win a $200 gift card! Click here to start the survey.

[Copilot]

@ArthurSonzogni 👋 This repository doesn't have Copilot instructions. With Copilot instructions, I can understand the repository better, work faster and produce higher quality PRs.

I can generate a .github/copilot-instructions.md file for you automatically. Click here to open a pre-filled issue and assign it to me. I'll write the instructions, and then tag you for review.

[ArthurSonzogni]

It looks like you added some build directories like build/_deps/...

[ArthurSonzogni]

You committed build artefects. They shouldn't be added.

[ArthurSonzogni]

You added the build/ directory, which contains build artifacts. That's wrong.

[ArthurSonzogni]

You shouldn't commit the build directory.