chore(labels): add severity low, high, and critical labels

[tusharmath]

Summary

Add three severity labels (severity: low, severity: high, severity: critical) to the GitHub labels configuration to enable better triage and prioritization of issues.

Context

The project's label system lacked a standardized way to communicate the impact level of bugs and issues. Without severity labels, it's difficult for contributors and maintainers to quickly assess which issues need urgent attention versus those that can be addressed later in the backlog.

Changes

• Added severity: low label (yellow #FFEB3B) — for minor issues that don't significantly affect functionality
• Added severity: high label (orange #FF9800) — for significant issues where core functionality is impaired
• Added severity: critical label (dark red #B71C1C) — for severe issues where the system is unusable or data is at risk
• Each label includes aliases for backward compatibility (severity:low, severity:high, severity:critical, critical)

Testing

Labels will be automatically synced to GitHub when the label sync workflow runs. You can verify the labels are applied correctly by checking the repository's Labels page after the workflow completes.

Links

• Labels configuration: .github/labels.json