Document Issue Duplication Detector workflow

[Copilot]

Added documentation for the Issue Duplication Detector workflow so users can discover and install it.

• README update

  • Added Issue Duplication Detector to the Depth Triage & Analysis workflow list with correct name and link.

• New docs page

  • Created docs/issue-duplication-detector.md describing purpose, install command, manual run, config path, and permissions.

• Workflow listing

  • Populated workflows/issue-duplication-detector.md with the full workflow definition for visibility alongside other compiled workflows.

Example install/run snippet:

# Add the workflow
gh aw add githubnext/agentics/issue-duplication-detector --pr

# Run it manually after merging
gh aw run issue-duplication-detector

Original prompt

Add Issue Duplicator to the README and relevant docs

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💡 You can make Copilot smarter by setting up custom instructions, customizing its development environment and configuring Model Context Protocol (MCP) servers. Learn more Copilot coding agent tips in the docs.