Remove snapshot URL sharing

[PengfanZ]

What changed

• remove read-only activity snapshot links, QR codes, legacy decoders, and the direct lz-string dependency
• make local sharing focus on starting a Live activity or exporting a balances-only PNG
• keep Live copy/QR invites, PWA link handoff, cached recovery copies, and explicit local duplication
• clear retired #share= fragments without reading them or changing local activity data
• update English and Simplified Chinese copy and project documentation

Why

Complete activities embedded in URLs grow with every expense and produce increasingly long links and dense QR codes. Live activities already provide the shorter, synchronized sharing path, while the balances-only export covers static results without exposing activity access.

Validation

• npm run typecheck
• npm run lint
• npm run test:coverage — 260 tests and 100% coverage
• npm run test:e2e — 12 Playwright flows
• npx supabase test db --local — 121 pgTAP tests
• Supabase advisors — no issues
• npm run build:pages