Add default Claude action

.github/workflows/claude-code.yml

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+name: Claude Code Review
+
+on:
+  issue_comment:
+    types: [created]
+  pull_request:
+    types: [opened, synchronize]
+
+jobs:
+  claude:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v3
+      - uses: anthropics/claude-code-action@beta
+        with:
+          anthropic_api_key: ${{ secrets.ANTHROPIC_API_KEY }}
+          experimental_allowed_domains: |
+            .github.com
+            .githubusercontent.com

CLAUDE.md

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+# CLAUDE.md
+Please review code for clarity, maintainability, and correctness. Suggest improvements without rewriting unless necessary.
+Avoid nitpicks unless they impact understanding.