Restructure codebase into separate website and calculator apps

[SakshiKekre]

Summary

Restructures the PolicyEngine app into a proper Turborepo monorepo with separate apps and shared packages.

New Structure

policyengine-app-v2/
├── apps/
│   ├── website/           # policyengine.org (port 3000)
│   └── calculator/        # app.policyengine.org (port 3001)
├── packages/
│   ├── design-system/     # Shared UI components and design tokens
│   └── shared/            # Common utilities, hooks, routing
└── app/                   # DELETED - old monolithic app

Key Changes

Apps separation:

• apps/website/ - Static website with NO Redux, NO React Query (lightweight)
• apps/calculator/ - Interactive calculator with full Redux + React Query stack

Shared packages:

• @policyengine/design-system - Design tokens, HomeHeader component, chart utilities
• @policyengine/shared - Country config, useCurrentCountry hook, geolocation routing, URL utilities

Code consolidation:

• Country labels consolidated to single source of truth in shared package
• HomeHeader refactored to "dumb" component accepting props (moved to design-system)
• Each app has thin wrapper components for app-specific navigation logic

New utilities:

• replaceCountryInPath() - Clean URL manipulation for country switching
• COUNTRIES / WEBSITE_COUNTRIES arrays for dropdowns
• countryLabels record for display names

Testing:

• Added organizations validation test (ensures all orgs have country IDs)
• Updated vitest.setup.ts with browser API mocks for Mantine components

Before Merging

1. Rebase after PR feat: Allow multiple instances of the dev server to run simultaneously #540 - That PR adds dynamic port discovery which resolves the dev mode cross-app URL issue.

2. Vercel Dashboard - Configure Root Directory for each project:

   • policyengine-website → apps/website
   • policyengine-calculator → apps/calculator

Documentation

See repo-code-split-summary.md for detailed breakdown of all changes.

Test Plan

• npm run typecheck passes
• npm run packages:build succeeds
• Website tests pass (npm test in apps/website)
• Website dev server runs on :3000
• Calculator dev server runs on :3001
• Vercel deployments succeed (requires dashboard config)
• Manual testing of both apps

[vercel]

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Project	Deployment	Review	Updated (UTC)
policyengine-app-v2	Error		Dec 28, 2025 10:19pm
policyengine-calculator	Error		Dec 28, 2025 10:19pm
policyengine-website	Error		Dec 28, 2025 10:19pm