refactor: modernize tooling and build system

- Migrate from npm to pnpm
- Replace CircleCI with GitHub Actions
- Replace ESLint + Prettier with oxlint + oxfmt
- Add ESM/CJS dual output support
- Update TypeScript target to ES2022
- Remove unused config files (Babel, TSLint, Renovate)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: takumi0h

.babelrc

@@ -1,6 +1,6 @@
 version: 2
 updates:
-  - package-ecosystem: "npm" # See documentation for possible values
-    directory: "/" # Location of package manifests
+  - package-ecosystem: "npm"
+    directory: "/"
     schedule:
-      interval: "daily"
+      interval: "weekly"

.circleci/config.yml

@@ -0,0 +1,25 @@
+name: CI
+
+on:
+  push:
+    branches: [master]
+  pull_request:
+    branches: [master]
+
+jobs:
+  ci:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+      - uses: pnpm/action-setup@v4
+      - uses: jdx/mise-action@v2
+      - uses: actions/setup-node@v4
+        with:
+          node-version-file: ".mise.toml"
+          cache: "pnpm"
+      - run: pnpm install --frozen-lockfile
+      - run: pnpm lint
+      - run: pnpm format:check
+      - run: pnpm check
+      - run: pnpm test
+      - run: pnpm build

.eslintrc.cjs

@@ -1,5 +1,6 @@
 node_modules
-npm-debug.log
 lib
+coverage
 .nyc_output
-coverage
+.DS_Store
+.claude

.github/dependabot.yml

@@ -0,0 +1,2 @@
+[tools]
+node = "24"

.github/workflows/ci.yml

@@ -11,14 +11,14 @@ $ npm install wareki
 ## Usage
 
 ```js
-import wareki from 'wareki'
+import wareki from "wareki";
 
-wareki('1989-01-07')
+wareki("1989-01-07");
 // -> 昭和64
-wareki('1989-01-08')
+wareki("1989-01-08");
 // -> 平成元
-wareki('2018-08-01', { unit: true })
+wareki("2018-08-01", { unit: true });
 // -> 平成30年
-wareki('2019-05-01')
+wareki("2019-05-01");
 // -> 令和元
 ```