Support priority labels on GitHub Issues #55

Problem

When syncing OpenSpec changes to GitHub Issues, there's no way to set priority labels (P0, P1, P2, P3) based on the change's priority.

Proposed Solution

Add a flag or read priority from the OpenSpec change metadata and apply the corresponding label when creating/updating GitHub Issues.

Use Case

BrickNow uses priority labels (P0-P3) to triage work. When creating a change with , the priority should propagate to the synchronized GitHub Issue.

Alternative

A config option in the specsync config file could map change metadata to labels.