feat: add adaptive SharedWorker inference topology

[aantenore]

Summary

• add adaptive page-owner and SharedWorker runtime selection with transactional commit semantics
• bind protocol traffic to deterministic runtime fingerprints and IndexedDB fencing epochs
• ship deterministic and live WebLLM worker labs with portable lifecycle fallback
• verify worker-safe package exports, Vite tarball consumption, preview behavior, and release version alignment

Validation

• pnpm check
• pnpm package:smoke
• pnpm audit --prod --audit-level=high
• 30/30 Playwright tests on Chromium, Firefox, and WebKit against development server
• 30/30 Playwright tests on Chromium, Firefox, and WebKit against production preview
• live WebLLM SharedWorker lifecycle test
• desktop and 390x844 visual QA with interaction proof

Boundaries

ServiceWorker ownership, cross-origin coordination, durable request replay after all clients close, and exactly-once provider side effects remain out of scope.