feat: add GitHub Actions workflow for automated gem releases

Triggers on version tags (v*) to:
- Run tests
- Build gem
- Push to RubyGems
- Create GitHub release with release notes

Requires RUBYGEMS_API_KEY secret to be configured.

Fixes #79

Author: cardmagic

.github/workflows/release.yml

@@ -0,0 +1,39 @@
+name: Release
+
+on:
+  push:
+    tags:
+      - 'v*'
+
+jobs:
+  release:
+    runs-on: ubuntu-latest
+    permissions:
+      contents: write
+      id-token: write
+
+    steps:
+    - uses: actions/checkout@v4
+
+    - name: Set up Ruby
+      uses: ruby/setup-ruby@v1
+      with:
+        ruby-version: '3.3'
+        bundler-cache: true
+
+    - name: Run tests
+      run: bundle exec rake test
+
+    - name: Build gem
+      run: gem build classifier.gemspec
+
+    - name: Push to RubyGems
+      env:
+        GEM_HOST_API_KEY: ${{ secrets.RUBYGEMS_API_KEY }}
+      run: gem push classifier-*.gem
+
+    - name: Create GitHub Release
+      uses: softprops/action-gh-release@v2
+      with:
+        files: classifier-*.gem
+        generate_release_notes: true