Migrate Danger to use danger-pr-comment workflow.

Replaces manual Danger setup with reusable workflow from numbata/danger-pr-comment, following the pattern from slack-ruby/slack-ruby-client#581 and slack-ruby/slack-ruby-bot-server#181.

- Add danger, danger-pr-comment, danger-changelog, and danger-toc to Gemfile
- Update Dangerfile to import danger-pr-comment and add changelog.check! and toc.check!
- Replace danger.yml workflow with reusable workflow pattern
- Add danger-comment.yml workflow for PR comments

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

Author: dblock

.github/workflows/danger-comment.yml

@@ -0,0 +1,11 @@
+name: Danger Comment
+
+on:
+  workflow_run:
+    workflows: [Danger]
+    types: [completed]
+
+jobs:
+  comment:
+    uses: numbata/danger-pr-comment/.github/workflows/danger-comment.yml@main
+    secrets: inherit

.github/workflows/danger.yml

@@ -1,22 +1,11 @@
----
-name: danger
-on: pull_request
+name: Danger
+on:
+  pull_request:
+    types: [opened, reopened, edited, synchronize]
 
 jobs:
   danger:
-    runs-on: ubuntu-latest
-    steps:
-    - uses: actions/checkout@v6
-      with:
-        fetch-depth: 100
-    - name: Set up Ruby
-      uses: ruby/setup-ruby@v1
-      with:
-        ruby-version: 3.4
-        bundler-cache: true
-    - name: Run Danger
-      run: |
-        # the token is public, has public_repo scope and belongs to the grape-bot user owned by @dblock, this is ok
-        TOKEN=$(echo -n Z2hwX2lYb0dPNXNyejYzOFJyaTV3QUxUdkNiS1dtblFwZTFuRXpmMwo= | base64 --decode)
-        DANGER_GITHUB_API_TOKEN=$TOKEN bundle exec danger --verbose
-
+    uses: numbata/danger-pr-comment/.github/workflows/danger-run.yml@main
+    secrets: inherit
+    with:
+      ruby-version: "3.4"

CHANGELOG.md

@@ -1,3 +1,9 @@
+### Next
+
+#### Features
+
+* [#970](https://github.com/ruby-grape/grape-swagger/pull/970): Migrate Danger to use danger-pr-comment workflow - [@dblock](https://github.com/dblock).
+
 ### 2.1.3 (2025-11-21)
 
 #### Features

Dangerfile

@@ -1,3 +1,6 @@
 # frozen_string_literal: true
 
-danger.import_dangerfile(gem: 'ruby-grape-danger')
+danger.import_dangerfile(gem: 'danger-pr-comment')
+
+changelog.check!
+toc.check!

Gemfile

@@ -45,7 +45,10 @@ group :development, :test do
 end
 
 group :test do
-  gem 'ruby-grape-danger', '~> 0.2', require: false
+  gem 'danger', require: false
+  gem 'danger-changelog', require: false
+  gem 'danger-pr-comment', require: false
+  gem 'danger-toc', require: false
   gem 'simplecov', require: false
   gem 'super_diff', require: false
 end