PostHog analytics reports: per-metric summary reports (like Viktor reports) #3824

Summary

Generate automated reports based on PostHog analytics that provide a per-metric summary — similar to how Viktor produces reports.

Motivation

Requested by @vaibhavski in #devs: surface PostHog usage data as structured, readable reports broken down by each metric.

Acceptance Criteria

• Connect to PostHog analytics data source
• Generate a summary report per metric
• Output format consistent with Viktor-style reports
• Reports can be triggered on demand (and/or scheduled)