feat(pmf): funnel instrumentation & conversion analytics

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Parent epic: PMF onboarding funnel (link below). Milestone M0.

Goal

Measure the funnel end-to-end so we can find PMF empirically, not by guessing.

Context

• Analytics infra exists (/v1/app/analytics/*, product-usage signals). Role-breakdown analytics is net-new (feat(ui): analytics role-specific breakdowns + cohorts #795).

Requirements / Deliverables

• Define + emit funnel events: landed → ran no-account tool → submitted PR → PR passed gate → saw conversion hook → registered → first reward.
• Per-step drop-off + conversion dashboard (extend analytics; relates feat(ui): analytics role-specific breakdowns + cohorts #795/feat(ui): maintainer repo/org quality dashboard #539).
• Cohort by repo (awesome-claude/gittensory/metagraphed) and by source (extension/CLI/MCP).

Outcome

A live conversion funnel we can watch and optimize weekly — the PMF feedback loop.

Depends on

P1, P2; relates #795 #539.

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Closing as not planned (2026-07-01 issue audit): Funnel/conversion analytics measure the retired PMF funnel (#799-801); superseded by the pivot.