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

[Unisay]

Brings this fork in line with the shared tooling canon and gives the AI coding agents a single source of truth.

CI (.github/workflows/ci.yml):

• Drop accept-flake-config = true. It let a PR's own flake nixConfig inject extra substituters and keys, which is a supply-chain risk; the caches are already pinned in extra_nix_config, so nothing is lost.
• luacheck now runs --std lua51 --no-unused-args instead of --std min. lua51 matches the actual target (it knows math.pow/math.atan2, which min flags), and --no-unused-args tolerates the curried fallback args the native FFI stubs ignore.
• Run the test step as bash ./scripts/test so it no longer depends on the file's execute bit.

AGENTS.md + CLAUDE.md:

• AGENTS.md is the one instruction file the coding agents read natively (Codex, Cursor, Copilot, Gemini CLI, Aider): the build/test/lint commands, the Lua 5.1 constraints, the FFI parenthesisation rule, and the toolchain pins.
• CLAUDE.md is a one-line @AGENTS.md import so Claude Code reads the same file instead of a second copy that drifts out of sync.

It also drops the dead bower.json, package.json left over from the JavaScript build; the toolchain is spago plus nix now.

Tooling and docs only, no src/ change, so there is no tag or package-set bump.

Verification

luacheck passes locally with --std lua51 --no-unused-args src/; the build runs green in CI.

[Copilot]

Pull request overview

This PR aligns CI and agent-facing documentation with the shared “hardened canon” for this PureScript→Lua fork, and removes legacy JS-era tooling files that are no longer used.

Changes:

• Harden CI Nix configuration by removing accept-flake-config = true, while keeping substituters/keys pinned via extra_nix_config.
• Make CI tooling match the project’s Lua 5.1 target (luacheck --std lua51 --no-unused-args) and run tests via bash ./scripts/test (no execute-bit dependency).
• Add a single source of truth for coding-agent instructions (AGENTS.md), and make CLAUDE.md import it; delete obsolete package.json/bower.json.

Reviewed changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
.github/workflows/ci.yml	Hardens Nix config and adjusts test + luacheck invocation to match Lua 5.1 + shell portability.
AGENTS.md	Adds unified agent instructions (commands, Lua 5.1 constraints, FFI parsing rule, toolchain pins).
CLAUDE.md	Imports AGENTS.md so Claude Code reads the same canonical instructions.
package.json	Removed legacy JS build tooling (pulp/psa/rimraf) no longer used.
bower.json	Removed legacy Bower manifest from the old JS-based PureScript workflow.

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