refactor: shared Google sign-in hook + remove Android false advertising #4752

Originally written by @ccantynz-alt on GitHub.
Imported from https://github.com/ccantynz-alt/voxlen/pull/49

Summary

• useGoogleSignIn shared hook — the identical useGoogleLogin block was copy-pasted across Navbar, Hero, Pricing, and CTA. Extracted into one hook, eliminating 60+ lines of duplication and ensuring all sign-in paths behave identically (including the id_token fallback that was missing from Hero/Pricing/CTA).
• Removed Android false advertising — Android is not built yet. Removed from: hero platform badges, hero subheadline, trust bar stat, platforms blurb, comparison section, pricing feature line, FAQ answer, and the Features card (changed to "iOS Keyboard Extension"). The Platforms section Android card correctly keeps its "Coming soon — join waitlist" badge.
• /api/me plan fix (from previous session) — returns actual plan from Voxlen JWT instead of hardcoded "admin"/"free".

Test plan

• Google sign-in works from Navbar, Hero, Pricing CTA, and bottom CTA
• No mention of Android as a live/available feature
• Android "Coming soon" card still visible in Platforms section with waitlist link
• Desktop app Account tab shows correct plan (pro/free_trial users see their plan)

https://claude.ai/code/session_011MFNHeFKrhfuSrEYVgrdyr

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