Cardano Updates

cachix/install-nix-action@v30 uses the Determinate Systems Nix installer
  which enables auto-optimise-store by default. This hard-links identical
  store files to a shared /nix/store/.links/<hash> location.

  On newer macOS, dyld resolves @loader_path using the canonical inode path
  rather than the path used to exec the binary. So when a haskell.nix-built
  binary (which links against libHSghc-boot dynamically) gets hard-linked
  into .links/, dyld sees it as living there and resolves @loader_path to
  /nix/store/.links/ — making the rpath @loader_path/../lib/aarch64-osx-ghc-9.6.7
  point to the non-existent /nix/store/lib/... instead of the actual GHC
  library directory.

  Setting auto-optimise-store = false prevents the hard-linking, keeping
  binaries at their proper store paths where @loader_path resolves correctly.

Following
https://arps18.github.io/posts/claude-code-mastery/#31-the-real-claudemd-from-the-claude-code-team
this adds a very simple CLAUDE.md.

I also add a CLAUDE.local.md; for me I think I will put in that:

```
- Don't ever commit or push; I'll do that manually
```

If you all agree these steps here are an absolute minimum, we can go
with it!

One annoying thing about the .local.md files is that you need to put
them in every worktree ( cc @v0d1ch ); so maybe it's of dubious value
anyway 🤷🏻 .

Note that this also changes the `just lint` step to use a separate
directory; so linting and regular building don't overwrite each other.

### Todo

- [x] Show an example of something maybe we'd like in a CLAUDE.local.md
file
- [x] Decide if this is really the _minimum_ (I'm happy with it; you can
decide by voting against the PR 😂 )
- [x] Check if the advice about the cabal repl is good enough

Signed-off-by: Sasha Bogicevic <[email protected]>