Add Duplicate Surfacing agentic workflow (pilot from winget-cli)

[denelon]

Description of the new feature / enhancement

Add the Duplicate Surfacing agentic workflow (GitHub Agentic Workflows / gh aw) to winget-create, mirroring the implementation now running in microsoft/winget-cli (PRs #6400, #6408, #6410).

When a new issue is opened, an agent searches existing issues and, if it finds a likely duplicate, applies a Possible-Duplicate label and posts an advisory comment linking the candidate for maintainer review. It is detect-only — it never closes issues or applies duplicate-close triggers.

This is the first Tier-1 pilot of rolling the workflow out across the winget repo family. Validating it here before replicating to the remaining code repos (winget-dsc, winget-cli-restsource, winget-command-not-found, winget-studio).

Proposed technical implementation details

• .github/workflows/duplicate-surfacing.md — the agentic workflow source (portable via ${{ github.repository }}).
• .github/workflows/duplicate-surfacing.lock.yml + .github/aw/actions-lock.json — compiled artifacts (gh aw compile).
• Includes both winget-cli refinements: no-op runs are not reported as tracking issues (noop.report-as-issue: false), and search guidance mandates high-recall in:title queries so old, sparse-body duplicates surface.
• Adds Possible-Duplicate label (amber #FBCA04, advisory).
• Adds autodetect, noop, PreIndexedPackage, toolsets to the spelling allow list.

Filed with GitHub Copilot assistance.