Add Docker support for multi-version Rails testing

- Add Dockerfile with Ruby 3.2 and required dependencies
- Add docker-compose.yml with services for Rails 6.1 and 7.0
- Add .dockerignore to exclude unnecessary files from Docker context
- Update .gitignore to use coverage/ directory and remove duplicate entry

This provides an easy way to test the gem with different Rails versions
in isolated Docker environments.

Author: takaokouji

.dockerignore

@@ -0,0 +1,35 @@
+# Git
+.git
+.gitignore
+.github
+
+# Claude/AI configuration
+.claude
+.serena
+CLAUDE.md
+
+# Documentation
+*.md
+!README.md
+
+# Test artifacts
+coverage/
+test_db
+*.sqlite3
+.last_run.json
+.resultset.json
+
+# Ruby/bundler
+.bundle
+vendor/bundle
+
+# OS files
+.DS_Store
+Thumbs.db
+
+# Editor files
+.vscode
+.idea
+*.swp
+*.swo
+*~

.gitignore

@@ -8,7 +8,7 @@
 Gemfile.lock
 InstalledFiles
 _yardoc
-coverage
+coverage/
 doc/
 lib/bundler/man
 pkg
@@ -17,7 +17,6 @@ spec/reports
 test/tmp
 test/version_tmp
 tmp
-coverage
 test/log
 test_db
 test_db-journal

Dockerfile

@@ -0,0 +1,22 @@
+# Dockerfile for testing jsonapi-resources with multiple Rails versions
+
+FROM ruby:3.2
+
+# Install dependencies
+RUN apt-get update -qq && \
+    apt-get install -y build-essential libpq-dev nodejs && \
+    apt-get clean && \
+    rm -rf /var/lib/apt/lists/*
+
+# Set working directory
+WORKDIR /app
+
+# Copy Gemfile and gemspec
+COPY Gemfile jsonapi-resources.gemspec ./
+COPY lib/jsonapi/resources/version.rb ./lib/jsonapi/resources/
+
+# Install bundler
+RUN gem install bundler
+
+# Note: bundle install will happen at runtime with specific RAILS_VERSION
+# This allows testing multiple Rails versions without rebuilding the image

docker-compose.yml

@@ -0,0 +1,39 @@
+services:
+  # Base service definition
+  test-base: &test-base
+    build:
+      context: .
+      dockerfile: Dockerfile
+    volumes:
+      - .:/app
+      - bundle-cache:/usr/local/bundle
+    working_dir: /app
+    stdin_open: true
+    tty: true
+
+  # Rails 6.1.7
+  rails-6.1:
+    <<: *test-base
+    container_name: jsonapi-rails-6.1
+    environment:
+      - RAILS_VERSION=6.1.7
+    command: bash -c "bundle update && bundle exec rake test"
+
+  # Rails 7.0.4
+  rails-7.0:
+    <<: *test-base
+    container_name: jsonapi-rails-7.0
+    environment:
+      - RAILS_VERSION=7.0.4
+    command: bash -c "bundle update && bundle exec rake test"
+
+  # Interactive shell for debugging (defaults to Rails 6.1)
+  shell:
+    <<: *test-base
+    container_name: jsonapi-shell
+    environment:
+      - RAILS_VERSION=${RAILS_VERSION:-6.1.7}
+    command: /bin/bash
+
+volumes:
+  bundle-cache: