fix: disable Privileged Mode + remove remaining BYOK + false claims cleanup #4757

Originally written by @ccantynz-alt on GitHub.
Imported from https://github.com/ccantynz-alt/voxlen/pull/44

Summary

• Privileged Mode disabled — toggle now shows "coming soon" and is non-interactive. Previously enabling it silently broke all dictation by forcing WhisperLocal (not yet implemented).
• BYOK fully removed — Settings panel and onboarding no longer show API key input fields. Users are directed to sign in with their Voxlen account.
• False advertising fixed — Comparison table, FAQ, and feature cards updated to reflect actual product state (offline mode and Android marked as coming soon, not live).
• React error #185 fixed — navigate() called in render body moved to useEffect.
• "Open App" broken link fixed — Was pointing to app.voxlen.ai (doesn't exist); now scrolls to #download.
• Stripe alert() removed — Replaced with smooth scroll to download/waitlist section.
• Grammar/translation silent failures — Now surface toast/inline errors to the user.
• Stale api.voxlen.com references — All updated to voxlen.ai/api.
• Prompt caching added to grammar API endpoint.

Test plan

• Sign in with Google on voxlen.ai — dashboard appears, no React errors
• Settings → Voxlen tab — only shows account sign-in, no API key fields
• Settings → Speech tab — Privileged Mode toggle is visibly disabled
• Pricing buttons with no Stripe config — scrolls to download section instead of alert()
• Grammar correction failure — shows error message rather than silently returning original text

https://claude.ai/code/session_011MFNHeFKrhfuSrEYVgrdyr

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