Add Claude Code GitHub workflow for @claude mentions (#231)

## Summary
- Adds GitHub Actions workflow to enable Claude Code integration via
@claude mentions
- Allows team to interact with Claude directly in PR and issue comments
- Provides AI assistance for code reviews, bug fixes, documentation, and
feature implementation

## What is Claude Code?

[Claude Code](https://claude.ai/code) is an AI coding agent that can
help with:
- Bug fixes and improvements  
- Documentation updates
- Implementing new features
- Code reviews and suggestions
- Writing tests
- And more\!

## How it works

Once this PR is merged, we'll be able to interact with Claude by
mentioning @claude in a pull request or issue comment. Claude will
analyze the comment and surrounding context, and execute on the request
in a GitHub action.

## Important Notes

- **This workflow won't take effect until this PR is merged**
- **@claude mentions won't work until after the merge is complete**
- The workflow runs automatically whenever Claude is mentioned in PR or
issue comments
- Claude gets access to the entire PR or issue context including files,
diffs, and previous comments

## Security

- Our Anthropic API key is securely stored as a GitHub Actions secret
- Only users with write access to the repository can trigger the
workflow
- All Claude runs are stored in the GitHub Actions run history
- Claude's default tools are limited to reading/writing files and
interacting with our repo by creating comments, branches, and commits
- We can add more allowed tools by modifying the workflow file

## Test plan
After merging this PR:
1. Create a test issue or PR
2. Add a comment mentioning @claude with a simple request
3. Verify Claude responds and the workflow runs successfully
4. Test on both issues and pull requests

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

.github/workflows/claude.yml

@@ -0,0 +1,63 @@
+name: Claude Code
+
+on:
+  issue_comment:
+    types: [created]
+  pull_request_review_comment:
+    types: [created]
+  issues:
+    types: [opened, assigned]
+  pull_request_review:
+    types: [submitted]
+
+jobs:
+  claude:
+    if: |
+      (github.event_name == 'issue_comment' && contains(github.event.comment.body, '@claude')) ||
+      (github.event_name == 'pull_request_review_comment' && contains(github.event.comment.body, '@claude')) ||
+      (github.event_name == 'pull_request_review' && contains(github.event.review.body, '@claude')) ||
+      (github.event_name == 'issues' && (contains(github.event.issue.body, '@claude') || contains(github.event.issue.title, '@claude')))
+    runs-on: ubuntu-latest
+    permissions:
+      contents: read
+      pull-requests: read
+      issues: read
+      id-token: write
+      actions: read # Required for Claude to read CI results on PRs
+    steps:
+      - name: Checkout repository
+        uses: actions/checkout@v4
+        with:
+          fetch-depth: 1
+
+      - name: Run Claude Code
+        id: claude
+        uses: anthropics/claude-code-action@beta
+        with:
+          anthropic_api_key: ${{ secrets.ANTHROPIC_API_KEY }}
+
+          # This is an optional setting that allows Claude to read CI results on PRs
+          additional_permissions: |
+            actions: read
+          
+          # Optional: Specify model (defaults to Claude Sonnet 4, uncomment for Claude Opus 4.1)
+          # model: "claude-opus-4-1-20250805"
+          
+          # Optional: Customize the trigger phrase (default: @claude)
+          # trigger_phrase: "/claude"
+          
+          # Optional: Trigger when specific user is assigned to an issue
+          # assignee_trigger: "claude-bot"
+          
+          # Optional: Allow Claude to run specific commands
+          # allowed_tools: "Bash(npm install),Bash(npm run build),Bash(npm run test:*),Bash(npm run lint:*)"
+          
+          # Optional: Add custom instructions for Claude to customize its behavior for your project
+          # custom_instructions: |
+          #   Follow our coding standards
+          #   Ensure all new code has tests
+          #   Use TypeScript for new files
+          
+          # Optional: Custom environment variables for Claude
+          # claude_env: |
+          #   NODE_ENV: test