chore(release): prepare 0.5.0

[mathiasbourgoin]

Summary

• bump dune-project and generated opam package versions to 0.5.0
• add public runtime version info through Miaou_core.Version
• add --version handling for runner CLIs before runtime initialization
• document 0.5.0 release notes and add version/CLI tests

Verification

• dune fmt
• dune build @ALL
• dune runtest
• dune build @install
• dune exec test/test_version.exe
• timeout 10s dune exec -- src/miaou_runner/miaou_runner_tui_main.exe --version
• timeout 10s dune exec -- src/miaou_runner/miaou_runner_native_main.exe --version

Both runner version commands print 0.5.0.