Upgrade Refstream agent sessions to alpha.4

[TeoSlayer]

Summary

• upgrade the optional Refstream renderer from alpha.2 to the verified alpha.4 browser release
• retain reusable agent handoffs, task IDs, progress, and collected answers across panel changes and reconnects
• save a tab-scoped, four-hour session snapshot for reload recovery while the local process remains live
• document connection, revocation, persistence, and privacy boundaries across the website, README, app, and agent guide
• prepare v0.15.0 without changing xterm.js as the default

Verification

• npm run check (94 root tests plus installer, Docker, deploy, QEMU manifest, SEO, mobile, and Formula checks)
• npm --prefix app test (841 passed, 3 skipped)
• VITE_FIREBASE_API_KEY=ci VITE_FIREBASE_AUTH_DOMAIN=ci.example.com VITE_FIREBASE_PROJECT_ID=ci VITE_FIREBASE_APP_ID=ci npm --prefix app run build
• npm run build:web
• npm run build:cli && npm run verify:downloads (78 release files)
• go test ./... and targeted race tests
• visual browser validation at desktop and 390×844, with no console errors