feat(analytics): PostHog product-analytics dashboard (/analytics, sase default)
Reusable AnalyticsDashboard over the locally-archived posthog_events stream
(~15min fresh, validated against live PostHog within 1%):
- KPIs with period-over-period deltas: visitors, signups, signup conversion,
trials, VIN decodes, parts views, OEM copies, WAU
- Activation funnel (signup cohort -> decode -> parts -> OEM)
- Conversion funnel (trial -> checkout -> payment)
- Acquisition by first-touch source (utm_source -> referrer -> direct)
- Daily trend + product quality (decode success %, empty-parts %, empty catalog)
Parameterized by projectKey (reusable across spokes); sase is the default.
Nav entry added. Reads posthog_events locally — no live PostHog API at render.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
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