Implement pagerduty.go notification

[gaurangkudale]

Overview

Implement the PagerDuty notification reporter using Events API v2.

Tasks

• Implement internal/reporter/pagerduty.go
• Trigger PD alert on P1/P2 incidents
• Resolve PD alert when incident auto-resolves
• Attach incident summary (ID, type, severity, signals) as alert detail
• Read API key from Kubernetes Secret (spec.notifications.pagerduty.secretRef)
• Configurable minimum severity to page (spec.notifications.pagerduty.severity)

Phase

Week 5 — Part of v0.1 Foundation notification layer.