Migrate Danger to danger-pr-comment workflow.

This PR completes the migration to the reusable danger-pr-comment workflow by adding the danger-comment.yml workflow file.

🤖 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

CHANGELOG.md

@@ -2,6 +2,7 @@
 
 #### 0.2.1 (Next)
 
+* [#6](https://github.com/slack-ruby/slack-ruby-bot-server-events-app-mentions/pull/6): Migrated Danger to danger-pr-comment workflow - [@dblock](https://github.com/dblock).
 * Your contribution here.
 
 #### 0.2.0 (2025/09/22)