feat(frontend): frontend workspace is a single component - bootstrap a real application shell #665

Summary

The entire frontend/ workspace currently consists of one component: frontend/src/components/analytics/OnboardingFunnelChart.tsx. There are no pages/routes, no API client, and no auth flow - yet CI builds and type-checks it, and the README describes a player-facing product (IQ survey onboarding, adaptive puzzles, leaderboards). The backend exposes the needed surface via its Swagger-documented REST API, so the gap is purely frontend scaffolding.

Proposal (phased)

Phase 1 - shell:

1. Confirm the stack implied by root dependencies (@tanstack/react-query, framer-motion) - i.e. a React/Vite app - and scaffold routing + layout.
2. Typed API client generated from the Swagger document (/api-json) or a hand-rolled fetch wrapper with error normalization.
3. Auth screens against the existing auth endpoints (Google OAuth server-side support exists via passport-google-oauth20; guest sessions via guest-session.provider.ts).

Phase 2 - core loops:
4. Puzzle browsing/solving view wired to puzzles + progress endpoints.
5. Streak & XP surfaces fed by streak/users endpoints.
6. Integrate the existing OnboardingFunnelChart into a dashboard route rather than leaving it orphaned.

Acceptance criteria

• npm --workspace frontend run dev serves a navigable app.
• Login (Google + guest) reaches the backend and stores tokens securely.
• One vertical slice (browse puzzle -> submit answer -> see XP/streak update) works end-to-end locally.