Traverse used JS implementation which is OK except that the array indexing was starting from 0.

Fix `traverse` failing at runtime

Follows the merged traverse fix (#2 by @Renegatto). On top of it:

- Fix mapWithIndexArray: it passed the 1-based Lua loop index to f, but
  PureScript mapWithIndex is 0-based, so f received i instead of i-1
  (originally reported in #1 by @sarahnya).
- Add a focused regression suite (test-regression/) run by scripts/test:
  traverse over Maybe is length/order-preserving at every size (>3 hits
  the pivot/append branch, which needs the Array Semigroup fix shipped in
  prelude v7.2.2), traverse over the Array applicative, and 0-based
  mapWithIndex.
- Align tooling: purescript-overlay dev shell on Lua 5.1 (drops easy-ps /
  insecure nodejs), canonical nix CI replacing the bower workflow,
  fail-fast scripts, and bump the package set to psc-0.15.15-20260614
  (prelude v7.2.2). Supersedes the earlier normalization PR #3.

Closes #1

chore: finalize traverse fix — mapWithIndex, regression test, tooling alignment

CI: drop accept-flake-config (supply-chain risk; caches already pinned),
run luacheck with --std lua51 --no-unused-args (matches the Lua 5.1 target
and the curried-FFI idiom), invoke the test step via bash so it no longer
needs the execute bit.

AGENTS.md is the single instruction file the coding agents read natively;
CLAUDE.md is a one-line @AGENTS.md import so Claude Code shares it. Also
removes dead JavaScript-era package files. Tooling and docs only, no src/.

chore: align CI to the hardened canon, add AGENTS.md

Repos moved from Unisay/* to the purescript-lua org. Update the pslua
flake input and lockfile owner (same rev 94c13ce), the packages.dhall
upstream-lua release URL, and the AGENTS.md links, so nothing relies on
the old-owner redirect.

chore: point pslua + package-set links at purescript-lua org

Wire treefmt via treefmt-nix: nixfmt, dhall format, purs-tidy (.tidyrc.json)
and LuaFormatter for the FFI (.lua-format, kept over StyLua because it
preserves the parentheses pslua's parser needs). `nix fmt` formats; the dev
shell installs a content-based pre-commit hook and CI runs
`nix fmt && git diff --exit-code` (content-based, since the in-place
formatters bump mtime and would trip treefmt --fail-on-change). Lua lines
budget 130 cols, matching the raised `luacheck --max-line-length`. The bulk
of the diff is the first format pass.

chore: add treefmt formatting (nix fmt + pre-commit + CI check)

Replace the dev-shell installer that wrote .git/hooks/pre-commit with a
tracked .githooks/pre-commit wired via `git config core.hooksPath .githooks`.

Fixes three issues with the old hook: it gated on `[ -d .git ]` (false in
worktrees/submodules where .git is a file), it clobbered any existing
.git/hooks/pre-commit on every `nix develop`, and `nix fmt … || exit 0`
swallowed real formatter failures. The new hook skips only when `nix` is
absent (CI is the authoritative gate) and otherwise blocks on a `nix fmt`
failure or reformat.

Toolchain consistency: pin the pslua dev flake input to the current
compiler main across the ecosystem. flake.lock only; the package set
consumes sources + FFI, not this dev input, so no re-tag is needed.