chore(ci): Migrate danger workflow from v2 to v3 (#93)

Converts danger workflow from reusable workflow (v2) to composite
action (v3). This is a breaking change that requires restructuring
the job definition.

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

Co-authored-by: Claude <noreply@anthropic.com>

Author: vaind

.github/workflows/danger.yml

@@ -6,4 +6,6 @@ on:
 
 jobs:
   danger:
-    uses: getsentry/github-workflows/.github/workflows/danger.yml@v2
+    runs-on: ubuntu-latest
+    steps:
+      - uses: getsentry/github-workflows/danger@v3