refactor: rebuild GPS discovery feed experience

[lizr-phys]

What changed

Rebuilds GPS around a focused, finite repository discovery feed while preserving all existing APIs, InteractionType semantics, search, library, trends, subscriptions, profile, bilingual mode, privacy controls, demo mode, and Site Agent.

Design and interaction

• Replaces the dashboard-like shell with a 76px desktop rail and independent mobile bottom navigation.
• Introduces a deterministic repository field passport with three-level progressive disclosure.
• Adds native accessible detail/negative-feedback dialogs, mobile bottom sheets, focus restoration, and reduced-motion support.
• Adds J/K/F/L/O/D/Z and / shortcuts with editable-target and dialog guards.
• Adds optimistic browse/feedback, immediate pending-request undo, truthful rollback, and stable toast status.
• Self-hosts Geist Variable for Latin text while retaining a system CJK stack.

Performance and resilience

• Health request count in the measured onboarding flow: 3 -> 1.
• Source CSS: 72,579 -> 56,352 bytes; production CSS: 66,191 -> 44,906 bytes.
• Inline styles: 133 -> 77; box-shadow declarations: 39 -> 18; backdrop-filter: 8 -> 0.
• Deduplicates and caches repository briefs, prefetches only the next item, and lazy-loads Site Agent.
• Cancels or isolates stale feed/search/detail/trend/agent responses.
• Keeps current content visible when an optimistic feedback write fails offline.

References and skills

Source patterns were studied from dub, Twenty, Karakeep, Bluesky Social, shadcn/ui, Magic UI, Motion, and TanStack Virtual. Applied frontend-design, impeccable, web-design-guidelines, and vercel-react-best-practices. No new npm runtime dependency was added.

Verification

• pnpm typecheck - pass
• pnpm lint - pass, 0 warnings
• pnpm test - 42/42 pass
• pnpm test:integration - 13/13 pass
• Targeted Chromium E2E - 4/4 pass (discovery/undo/mobile dialog, Site Agent, mobile onboarding, Axe/reduced motion/offline recovery)
• pnpm build - pass, 37 routes/pages, 37.2s total, 9.8s compile
• Impeccable finish review - disposition: pass

Screenshots

Additional captures: project detail (mobile, zh), search (desktop, en), and feed error recovery (desktop, en) are in docs/screenshots/.

Compatibility and known limits

• Search/recommendation ranking weights and backend business semantics are unchanged.
• Chromium was the scoped E2E browser for this frontend round; the complete cross-browser device matrix remains follow-up validation.
• Brief cache is process-local and should move to Redis/KV for multi-instance deployments.
• Preview: Vercel deployment was intentionally skipped per user request. Local production smoke test passed at http://localhost:3200 (home 200, health ok, Demo start 200).

Full report: docs/frontend-redesign-report.md
Design system: DESIGN.md