Modernize frontend code

[jake-low]

This PR cleans up and modernizes a bunch of things on the OSMCha frontend, in order to make development easier.

Notable changes:

• Switch from Yarn to npm (npm comes with Node and has all the features we need; using it makes things easier for first-time contributors)
• Port all Flow code to TypeScript (TS has decisively won as the preferred typed JS flavor)
• Switch from react-scripts (the build tool from the deprecated create-react-app project) to Vite
• Switch from Jest to Vitest, and simplify other testing dependencies
• Switch from Prettier + ESLint to Biome
• Upgrade to React 18
• Upgrade to react-router v7
• Remove Redux and Immutable.js dependencies; rewrite state management using React hooks or Zustand (for persistent state) and port data fetching from Redux Sagas to TanStack Query.
• Refactor npm scripts to make building, running, testing, linting, and formatting easier.

The goal of all of this is to make contributing to OSMCha easier and more fun. Community contributions to OSMCha are more than welcome, and there's no shortage of open issues to work on if you'd like to get involved.

P.S. - These efforts are possible because OSMCha is a program of OpenStreetMap US now, which allows me (as a staff member of the organization) to spend some of my time working on maintenance. I plan to continue to work on other improvements for OSMCha in the near future.