Upgrade to Next 16 + React 19

[MaxGhenis]

Summary

• Upgrade next from ^14.2 to ^16 (resolved to 16.1.6)
• React was already at ^19.2.3, no change needed
• Tailwind 4 already in place, no changes needed
• Build passes cleanly with Turbopack

Test plan

• bun run build succeeds with no errors
• Verify Vercel deployment works

🤖 Generated with Claude Code

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Project	Deployment	Actions	Updated (UTC)
snap-bbce-repeal	Ready	Preview, Comment	Mar 7, 2026 1:49pm

[MaxGhenis]

Closing as stale (2 months without updates and likely conflicts with main). The framework upgrade goal here — Next 14 → 16, React 18 → 19, Tailwind 3 → 4 — is still valid and overlaps with the broader Next-modernization sweep happening across the org (see policyengine-ui-kit#28 → 0.8.0+0.9.0 and the consumer rollout). I'll re-open a fresh PR on top of current main when this repo's turn comes up. If you want it sooner, ping me.