Migrate Danger to use danger-pr-comment workflow.

Updated to use the numbata/danger-pr-comment reusable workflow pattern,
replacing manual Danger setup with cleaner workflow delegation. This brings
the implementation in line with slack-ruby/slack-ruby-client#581 and
slack-ruby/slack-ruby-bot-server#181.

Changes:
- Updated danger.yml to use danger-run.yml reusable workflow
- Added danger-comment.yml workflow for posting PR comments
- Updated Dangerfile to import danger-pr-comment gem and use changelog.check! and toc.check!
- Added danger-pr-comment gem to Gemfile.danger
- Updated Ruby version from 2.7 to 3.4

🤖 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@v0.1.0
+    secrets: inherit

.github/workflows/danger.yml

@@ -1,22 +1,14 @@
 ---
-name: danger
-on: [pull_request]
+name: Danger
+
+on:
+  pull_request:
+    types: [opened, reopened, edited, synchronize]
+
 jobs:
   danger:
-    runs-on: ubuntu-latest
-    env:
-      BUNDLE_GEMFILE: Gemfile.danger
-    steps:
-    - uses: actions/checkout@v2
-      with:
-        fetch-depth: 0
-    - name: Set up Ruby
-      uses: ruby/setup-ruby@v1
-      with:
-        ruby-version: 2.7
-        bundler-cache: true
-    - name: Run Danger
-      run: |
-        # the personal token is public, this is ok, base64 encode to avoid tripping Github
-        TOKEN=$(echo -n Z2hwX0xNQ3VmanBFeTBvYkZVTWh6NVNqVFFBOEUxU25abzBqRUVuaAo= | base64 --decode)
-        DANGER_GITHUB_API_TOKEN=$TOKEN bundle exec danger --verbose
+    uses: numbata/danger-pr-comment/.github/workflows/danger-run.yml@v0.1.0
+    secrets: inherit
+    with:
+      ruby-version: '3.4'
+      bundler-cache: true

Dangerfile

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

Gemfile

@@ -25,6 +25,10 @@ gemspec
 group :development, :test do
   gem 'bundler'
   gem 'database_cleaner'
+  gem 'danger'
+  gem 'danger-changelog', require: false
+  gem 'danger-pr-comment', require: false
+  gem 'danger-toc', require: false
   gem 'fabrication'
   gem 'faker'
   gem 'hyperclient'