Add automated duplicate issue detection (#8171)

## Summary
Implements automated detection of potential duplicate issues using
GitHub Actions.

## Implementation Details
- Uses `wow-actions/potential-duplicates@v1` action
- Triggers on issue `opened` and `edited` events
- Configured with **90% similarity threshold** to minimize false
positives
- Automatically adds `potential-duplicate` label and comment with links
to similar issues

## Rationale for 90% Threshold
Based on manual testing with the `gh_tool` CLI:
- 85% threshold produced too many false positives from template-based
matches
- True duplicates typically have 90%+ similarity
- Uses Damerau-Levenshtein distance algorithm (same as manual tool)

## Testing
- ✅ YAML syntax validated
- ✅ Pre-commit hooks passed (lint + ts-check)
- ✅ Created `potential-duplicate` label in repository
- Manual testing of similar configuration showed good results at 90%
threshold

## Dependencies
- Depends on #8166 (add-gh-tools-cli branch) being merged first
- This PR adds the automation layer on top of the manual tooling

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

---------

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

.github/workflows/duplicate-detection.yml

@@ -0,0 +1,36 @@
+# This workflow automatically detects potential duplicate issues
+# using text similarity analysis with Damerau-Levenshtein distance.
+#
+# For more information, see: https://github.com/wow-actions/potential-duplicates
+
+name: Duplicate Issue Detection
+on:
+  issues:
+    types: [opened, edited]
+
+jobs:
+  detect-duplicates:
+    runs-on: ubuntu-latest
+    # Only run on issues, not pull requests
+    if: ${{ !github.event.issue.pull_request }}
+    steps:
+      - uses: wow-actions/potential-duplicates@v1
+        with:
+          GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
+          # Use 90% similarity threshold to reduce false positives from template matches
+          # Testing showed that 85% threshold produced too many template-based matches
+          # True duplicates typically have 90%+ similarity
+          threshold: 0.90
+          # Comment on the issue if duplicates are found
+          label: potential-duplicate
+          # Custom comment to link to potentially duplicate issues
+          comment: |
+            **Potential duplicate detected**
+
+            This issue appears to be similar to existing issues. Please review them before continuing:
+
+            {{#issues}}
+            - [#{{number}}]({{html_url}}) ({{accuracy}}% similar)
+            {{/issues}}
+
+            If this is not a duplicate, please clarify how it differs from the above issues.