ci: add focused Claude workflows with context-aware prompts

Add claude-mention.yml for @claude mentions in issues/PRs and
claude-pr-review.yml for automatic PR reviews.

Key improvements:
- claude-mention: Triggers on @claude with project-specific prompt
- claude-pr-review: Auto-reviews PRs from new contributors with CONTRIBUTING.md criteria
- Both workflows: Restricted permissions (read-only contents, no merge capability)

🤖 Generated with Claude Code (https://claude.ai/code)
Co-Authored-By: Claude <noreply@anthropic.com>

.github/workflows/claude-mention.yml

@@ -0,0 +1,45 @@
+name: Claude Mention
+
+on:
+  issue_comment:
+    types: [created]
+  pull_request_review_comment:
+    types: [created]
+  issues:
+    types: [opened, assigned]
+  pull_request_review:
+    types: [submitted]
+
+jobs:
+  claude-mention:
+    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 # Cannot merge PR
+      pull-requests: write
+      issues: read
+      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@v1
+        with:
+          # See https://github.com/anthropics/claude-code-action/blob/main/docs/usage.md
+          anthropic_api_key: ${{ secrets.ANTHROPIC_API_KEY }}
+          additional_permissions: |
+            actions: read
+          prompt: |
+            If this is a PR adding a project or library, review against CONTRIBUTING.md criteria.
+            Otherwise, follow the instructions in the comment or issue that tagged you.

.github/workflows/claude-pr-review.yml

@@ -0,0 +1,43 @@
+name: Claude PR Review
+
+on:
+  pull_request:
+    types: [opened, synchronize, ready_for_review, reopened, labeled]
+    paths:
+      - "README.md"
+
+jobs:
+  claude-pr-review:
+    if: |
+      github.event.label.name == 'claude-review' ||
+      github.event.pull_request.author_association == 'FIRST_TIME_CONTRIBUTOR' ||
+      github.event.pull_request.author_association == 'FIRST_TIMER' ||
+      github.event.pull_request.author_association == 'NONE'
+
+    runs-on: ubuntu-latest
+
+    permissions:
+      contents: read # Cannot merge PR
+      pull-requests: write
+      issues: read
+      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 Review
+        id: claude-review
+        uses: anthropics/claude-code-action@v1
+        with:
+          # See https://github.com/anthropics/claude-code-action/blob/main/docs/usage.md
+          anthropic_api_key: ${{ secrets.ANTHROPIC_API_KEY }}
+          plugin_marketplaces: "https://github.com/anthropics/claude-code.git"
+          plugins: "code-review@claude-code-plugins"
+          prompt: |
+            Review this PR against the acceptance criteria in CONTRIBUTING.md.
+            Focus on: Industry Standard, Rising Star, or Hidden Gem criteria.
+            Check for automatic rejection reasons (abandoned, duplicates, spam).
+            /code-review:code-review ${{ github.repository }}/pull/${{ github.event.pull_request.number }}