0.4.3

fix(ci): release.yml reads VERSION from src/core/config.cppm (#224)

The Determine version step was looking at the pre-restructure path
`core/config.cppm`. After the C++23 module restructure that moved
sources under `src/`, the sed read produces an empty string and the
silent fallback `[[ -z "$VER" ]] && VER="0.2.0"` kicked in. Result:
the v0.4.3 release attempt instead tagged as v0.2.0 and softprops
appended the 0.4.3 archives onto the existing 2026-02-24 v0.2.0
release.

Two-line fix:

  - core/config.cppm  → src/core/config.cppm
  - silent default → hard failure (so the next time someone moves
    the file, the release run fails loudly instead of silently
    poisoning an old tag)

Verified locally:

  $ sed -n 's/.*VERSION = "\([^"]*\)".*/\1/p' src/core/config.cppm
  0.4.3