multi: add issue dedupe command and workflow

- add /dedupe command definition for Claude Code
- add workflow to run dedupe on issue opened
- add comment helper script for posting duplicates

.github/workflows/claude-dedupe-issues.yml

@@ -0,0 +1,34 @@
+name: Claude Issue Dedupe
+description: Automatically dedupe GitHub issues using Claude Code
+on:
+  issues:
+    types: [opened]
+  workflow_dispatch:
+    inputs:
+      issue_number:
+        description: 'Issue number to process for duplicate detection'
+        required: true
+        type: string
+
+jobs:
+  claude-dedupe-issues:
+    runs-on: ubuntu-latest
+    timeout-minutes: 10
+    permissions:
+      contents: read
+      issues: write
+      id-token: write
+
+    steps:
+      - name: Checkout repository
+        uses: actions/checkout@v4
+
+      - name: Run Claude Code slash command
+        uses: anthropics/claude-code-action@v1
+        env:
+          GH_TOKEN: ${{ secrets.GITHUB_TOKEN }}
+        with:
+          github_token: ${{ secrets.GITHUB_TOKEN }}
+          allowed_non_write_users: "*"
+          prompt: "/dedupe ${{ github.repository }}/issues/${{ github.event.issue.number || inputs.issue_number }}"
+          claude_code_oauth_token: ${{ secrets.CLAUDE_CODE_OAUTH_TOKEN }}