Migrate server app to Fresh 2.x

[kellnerd]

https://fresh.deno.dev/docs/migration-guide

I initially chose Fresh 1.x because it is simple, fast and has almost no dependencies, so I'm still a bit skeptical about the vite builder dependency of Fresh 2.
Therefore I've been hesitant to upgrade to 2.x because I didn't want to introduce a dependency to vite and there is no migration guide for just pure Fresh 2.
Now that fresh plans to remove the 1.x legacy builder in favor of vite, there is probably no point in experimenting with Fresh 2 without vite.

Some advantages and unblocked tasks for Harmony:

• It will be easier to compose (Express.js-like) middleware functions, which will help for Add an api for external apps #107
• Fresh 2.x is on jsr.io, so we can finally migrate all(?) dependencies (including those of Fresh) from URL specifiers (deno.land, esm.sh) to JSR (or npm)
  • Re-enable the lock file (which caused issues with mutable URL dependencies)
  • Publish Harmony providers and core logic on JSR (package = everything minus the web app?)

[kellnerd]

This announcement confirms both that fresh without vite has no future and that fresh with vite still seems to have its flaws.