feat(pmf): extension on-ramp flow for non-registered users

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

Goal

Make the shipped browser extension (#534) the on-GitHub on-ramp: a stranger browsing a gittensory-enabled repo sees the no-account value (P1) and the conversion hook (P2) in context.

Context

• Extension shipped: apps/gittensory-extension/ (feat(extension): rebuild as dual-audience overlay (WXT + React) #534). /v1/extension/pull-context endpoint exists (feat(api): /v1/extension/* contributor-context endpoints + miner auth scope #556/PR feat(api): /v1/extension/* contributor-context endpoints + miner auth scope #723).
• Today the extension assumes an authenticated/maintainer-ish context; need an anon-friendly path.

Requirements / Deliverables

• Anon-visible overlay on issues/PRs: 'good first issue' fit, anti-slop self-check, contribution guidance — no login required.
• Inline conversion hook (P2) at the quality-PR moment.
• One-tap 'register on gittensor' from the overlay.

Outcome

The extension converts passive GitHub browsing on owned repos (awesome-claude/gittensory/metagraphed) into funnel entries.

Depends on

P1, P2, #534, #556.

[JSONbored]

Closing as not planned (2026-07-01 issue audit): Extension anon on-ramp is the retired non-registered-conversion funnel.