ci: replace prettier with biome (#16)

Replace the repo's Prettier wiring in pre-commit and quality CI with
Biome. Add a minimal `biome.json` for this repo and scope the Biome
checks to the JSON files it can actually format here.

Verified locally with `pnpm dlx @biomejs/biome@2.4.13 format .` and
`pre-commit run --all-files`.

Author: barrettruth

biome.json

@@ -0,0 +1,16 @@
+{
+  "$schema": "https://biomejs.dev/schemas/2.4.13/schema.json",
+  "vcs": {
+    "enabled": true,
+    "clientKind": "git",
+    "useIgnoreFile": true
+  },
+  "files": {
+    "ignoreUnknown": true
+  },
+  "formatter": {
+    "enabled": true,
+    "indentStyle": "space",
+    "indentWidth": 2
+  }
+}

flake.nix

@@ -23,7 +23,7 @@
         default = pkgs.mkShell {
           packages = [
             pkgs.just
-            pkgs.prettier
+            pkgs.biome
             pkgs.stylua
             pkgs.neovim
             pkgs.selene
@@ -35,7 +35,7 @@
         ci = pkgs.mkShell {
           packages = [
             pkgs.just
-            pkgs.prettier
+            pkgs.biome
             pkgs.stylua
             pkgs.neovim
             pkgs.selene

justfile

@@ -4,7 +4,7 @@ default:
 format:
     nix fmt -- --ci
     stylua --check .
-    prettier --check .
+    biome format .
 
 lint:
     git ls-files '*.lua' | xargs selene --display-style quiet