fix: prevent duplicate PR check from flagging current PR as duplicate

[Raviguntakala]

Problem

When a new PR is opened, the duplicate PR detection workflow searches for similar PRs. However, the search results include the newly opened PR itself, causing it to be incorrectly flagged as a "duplicate" of itself.

Solution

• Added excludePR parameter to the github-pr-search tool to filter out a specific PR
• Updated the workflow to pass the current PR number explicitly via CURRENT_PR_NUMBER
• Updated agent instructions to use this parameter