Root cause: devenv shell reads devenv.nix only; IHP's Haskell setup is in
flake.nix's devenv.shells.default which is only loaded by nix develop.
Fix: create devenv.yaml to register IHP as a devenv input (pinned to the
same rev as flake.lock) with overlays.default applied. Update devenv.nix
to set IHP_LIB/IHP env vars and enable languages.haskell with pkgs.ghc
(IHP-overlay GHC) + all project packages; add ghcid explicitly.
devenv.lock pins IHP at df3922d (matches flake.lock).
scripts/compile-check: updated header comments and added IHP_LIB echo;
switches from ghcid to ghci one-shot (ghcid not available in all shells).
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
