chore: add Biome linter + format all code + CI lint step (#26)

- biome.json: 2-space indent, single quotes, recommended rules
- All 30 source files formatted (auto-fix, no logic changes)
- CI: Biome lint runs before type check and tests
- Root package.json with lint/lint:fix scripts

89 unit tests green (82 core + 7 watcher).

小橘 🍊（NEKO Team）

Co-authored-by: 小橘 <xiaoju@shazhou.work>

package.json

@@ -0,0 +1,10 @@
+{
+  "private": true,
+  "scripts": {
+    "lint": "biome check packages/",
+    "lint:fix": "biome check --write packages/"
+  },
+  "devDependencies": {
+    "@biomejs/biome": "^2.4.11"
+  }
+}