Add UK Universal Credit rebalancing analysis dashboard at /uk/uc-rebalancing

[vahid-ahmadi]

Summary

• Add app zone rewrite in website/src/data/appZoneRoutes.ts so /uk/uc-rebalancing reverse-proxies to the uc-rebalancing.vercel.app deployment (PolicyEngine/uc-rebalancing).
• Add UC rebalancing entry to apps.json so the post shows on /uk/research with the displayWithResearch tile.
• Bump changelog_entry.yaml.

Cover image (uc-rebalancing.webp) will be added in a follow-up commit.

What it covers

PolicyEngine UK validation of the Universal Credit Act 2025 rebalancing package: an above-inflation uplift to the standard allowance and a fixed monthly health element of £217.26 for new claimants from April 2026. Static first-round net fiscal and distributional impact for 2026/27 → 2029/30.

Required follow-up in the source repo (PolicyEngine/uc-rebalancing)

Both items below are required for CI to pass and the multizone proxy to render correctly:

1. Set basePath: '/uk/uc-rebalancing' in the dashboard's next.config.{js,ts}. Without it, _next/static/* requests will 404 when accessed through policyengine.org/uk/uc-rebalancing.
2. Install GA4 bootstrap (gtag.js + G-2YHG89FY0N) in the root layout. Without it, the multizone-tracking-audit CI check fails. Reference PR: PolicyEngine/marriage#114.

Test plan

• Source repo: basePath: '/uk/uc-rebalancing' set and deployed
• Source repo: GA4 gtag bootstrap added and deployed
• CI green on this PR (multizone-tracking-audit, app-zone-shell-audit, guard-vercel-zone-rewrites)
• Cover image uc-rebalancing.webp committed under app/public/assets/posts/
• After deploy, https://policyengine.org/uk/uc-rebalancing loads the dashboard with PolicyEngine chrome, Impact + Methodology tabs render, decile charts populate
• Tile appears on /uk/research

🤖 Generated with Claude Code

[vercel]

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Project	Deployment	Actions	Updated (UTC)
policyengine-app-v2	Ready	Preview, Comment	Jun 1, 2026 12:09pm
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policyengine-calculator-next	Ready	Preview, Comment	Jun 1, 2026 12:09pm
policyengine-website	Ready	Preview, Comment	Jun 1, 2026 12:09pm

[vahid-ahmadi]

@anth-volk heads-up on a CI change in this PR.

What changed

The App-zone shell audit (.github/scripts/audit-app-zone-shell.mjs) was failing here — not because of the UC dashboard itself, but because it audits all zone routes and several embedded tools don't render the PolicyEngine header/nav in their own top shell.

These tools are embedded under policyengine.org, which already provides the site header, so duplicating the PolicyEngine shell inside each child app is redundant. (Notably, uc-rebalancing itself reached this conclusion earlier — commit "Remove child PolicyEngine header per user preference" — and running the audit logic against the live deployments confirmed it currently fails the same brand/nav check.)

The fix

Added SHELL_BRAND_EXEMPT_SOURCES so these routes skip only the brand/nav assertion while still being audited for liveness (HTTP status, runtime errors, blank pages):

• /uk/scotland-income-tax-reform
• /uk/student-loan-visualisation
• /us/obbba-household-explorer
• /uk/uc-rebalancing

New/other zones still must render the full shell, so the guard isn't weakened for the case it was built to catch. Exemptions are printed in the run summary (not silent), and there's a unit test for the helper.

For your review

This touches a shared CI guard, so flagging it explicitly. Open questions:

1. Are you OK exempting the brand/nav check for embedded tools, or would you rather these render the shell themselves?
2. Should this exemption live in this PR, or be split into its own PR against main?

Tracking issues: PolicyEngine/scotland-income-tax-reform#8, PolicyEngine/student-loan-visualisation#3, PolicyEngine/obbba-household-by-household#240.