feat(nix): add official Nix/NixOS support with auto-update workflow

[realitymolder]

Add a flake + nix/package.nix derivation building Terax for x86_64-linux, x86_64-darwin, and aarch64-darwin, with nixosModules and darwinModules for easy system integration.

Extract version and SRI hashes into nix/sources.json consumed by the derivation via builtins.fromJSON, and add a GitHub Actions workflow triggered on release published that downloads assets, computes SRI hashes, and opens a PR bumping sources.json automatically.

What

Add official Nix/NixOS support via a flake + nix/package.nix derivation, and a release workflow to keep the Nix sources up to date automatically.

• flake.nix / nix/package.nix — builds Terax for x86_64-linux, x86_64-darwin, aarch64-darwin; includes nixosModules and darwinModules for easy system integration
• nix/sources.json — standalone version/hashes file consumed by the derivation
• .github/workflows/update-nix-sources.yml — triggers on release published, downloads assets, computes SRI hashes, and opens a PR bumping sources.json

Why

Nix was not previously supported as an installation method. Manual bumping of version + three hashes on every release is also error-prone — the workflow automates it.

How

builtins.fromJSON (builtins.readFile ./sources.json) loads version and per-platform hashes. The release workflow uses openssl dgst -sha256 -binary + base64 to produce SRI hashes matching Nix's sha256-... format. The flake provides packages.terax, nixosModules.terax, and darwinModules.terax.

Testing

• nix build .#terax succeeds on Linux and macOS
• nix/package.nix parses correctly — builtins.fromJSON reads the file at evaluation time
• Workflow syntax validated against peter-evans/create-pull-request@v7
• README updated with Nix install instructions pointing to the official flake

Notes for reviewer

First-class Nix support for the project — the flake is the canonical way to install on NixOS.