feat(report): output human summary + machine-readable incident artifact

[sonwr]

Goal

Provide dual-output reporting for operators and automation.

Scope

• Human summary: one-line reason + action hint
• JSON artifact: incidentReason, riskTier, confidence, recommendedActions
• Stable output schema for CI integrations

Acceptance Criteria

• Snapshot tests for output shape
• Example report fixtures in docs
• Backward-compatible field naming rules