Maintenance release v0.2.0 — modernize project tooling

- Replace Indexer metadata with standard gemspec
- Add Rakefile and minitest test suite (6 tests)
- Rewrite README with Clap-vs-CLI.K feature comparison
- Add GitHub Actions CI (Ruby 3.1–3.4)
- Require Ruby >= 3.1

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: trans

.gemspec

@@ -0,0 +1,21 @@
+name: Test
+
+on:
+  push:
+    branches: [master]
+  pull_request:
+    branches: [master]
+
+jobs:
+  test:
+    runs-on: ubuntu-latest
+    strategy:
+      matrix:
+        ruby: ['3.1', '3.2', '3.3', '3.4']
+    steps:
+      - uses: actions/checkout@v4
+      - uses: ruby/setup-ruby@v1
+        with:
+          ruby-version: ${{ matrix.ruby }}
+          bundler-cache: true
+      - run: bundle exec rake test

.github/workflows/test.yml

@@ -1,10 +1,7 @@
-.ergo/digest
 .yardoc
-doc/
-log/
-pkg/
-tmp/
-web/
-/QED.md
-*.lock
+doc
+log
+pkg
+tmp
+Gemfile.lock
 *.gem