[WEB-5040] feat: admin react-router migration

[lifeiscontent]

Description

This pull request migrates the admin application from Next.js to a React Router + Vite architecture.
It replaces server-side rendering with a modern client-side routing setup and static asset build flow.

Key updates include:

• Removal of Next.js dependencies, configuration files, and SSR-specific logic.
• Introduction of React Router for route definitions, nested layouts, and navigation handling.
• Integration of Vite for faster local development and optimized production builds.
• Setup of a static asset server (e.g. nginx) for production deployment of admin builds.
• Addition of a dedicated 404 page and consistent page metadata (titles/descriptions).
• Compatibility layers for next/link, next/image, and related utilities to ensure smooth migration.
• Adjusted Dockerfile, nginx configuration, and build scripts to reflect new asset structure.
• Type, asset, and path import fixes across the admin app.

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Type of Change

• Bug fix (non-breaking change which fixes an issue)
• Feature (non-breaking change which adds functionality)
• Improvement (change that would cause existing functionality to not work as expected)
• Code refactoring
• Performance improvements
• Documentation update

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Screenshots and Media (if applicable)

N/A — migration affects build and routing structure, not UI appearance.

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Test Scenarios

• Verified all admin routes (login, dashboard, settings, workspace management) work as expected using React Router.
• Confirmed page metadata updates properly (titles/descriptions).
• Tested 404 handling for invalid routes.
• Validated Vite build output and confirmed assets serve correctly via nginx.
• Verified Docker build and run process produces correct static deployment.
• Checked authentication flow and UI theming for regressions.
• Ensured all type checks, linting, and import paths pass after migration.

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References

https://app.plane.so/plane/browse/WEB-5169/

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Summary by CodeRabbit

• New Features

  • Admin migrated to React Router with an Express server, Next.js compatibility shims, route metadata, a custom 404 page, and a top progress bar.

• Bug Fixes

  • Fixed admin license redirect paths to include trailing slashes.

• Refactor

  • Reworked admin build and runtime for static asset serving; simplified many layouts and navigation.

• Chores

  • Updated package scripts, build tooling, typings, asset handling, exports, and added progress bar CSS.

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Note

Migrates the admin app from Next.js SSR to React Router + Vite with a static build served via nginx, adds routing/meta/404, dev Express server with API proxy, and fixes admin redirects to trailing-slash paths.

• Admin (frontend):
  • Replace Next.js with React Router + Vite: new app/root.tsx, app/routes.ts, providers, RR Outlet, and meta exports across pages.
  • Add Next.js shims (app/compat/next/*) for link, image, navigation; convert assets to ?url imports; remove page layout.tsx files.
  • Add top navigation progress bar (core/lib/b-progress) and dedicated components/404.tsx.
• Build & Deploy:
  • Add vite.config.ts, react-router.config.ts, Express server (server.mjs, server/app.ts) with API proxy; update package.json scripts.
  • Overhaul Dockerfile.admin to build static assets and serve via nginx (nginx/nginx.conf at /god-mode); add healthcheck.
  • Update ignores (.dockerignore, .gitignore) and Tailwind/PostCSS wiring.
• Backend:
  • Adjust admin signup/signin redirects to general/ (trailing slash).
• Packages/Tooling:
  • Update eslint config versions; add router/vite/express deps; minor exports for @plane/editor/@plane/propel styles.

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