fix: render returning visitor landing immediately

[ShuhaoZhangTony]

What changed

• render the returning-visitor welcome identity and seed questions before remote initialization
• preserve onboarding-first behavior for new visitors
• add desktop and 390x844 gates with a deliberately blocked versions endpoint
• release v4.6.30 with app.4222.js/styles.4222.css

Root cause

The useful static landing content was unhidden only after sequential version, health, admin-session, and user-session requests. Slow public initialization therefore left an otherwise healthy page looking empty.

Validation

• 17/17 frontend contracts
• 17/17 Firefox interaction/theme tests
• Ruff clean
• 722 passed, 28 skipped full Python suite

Closes #14