Establish bun monorepo

[ebma]

This pull request adds changes to use bun throughout the whole repository. It also replaces prettier and eslint with biome, a tool that is able to do it all in one.

The most important changes summarized:

• executable projects, namely 'frontend' and 'api', were moved to the 'apps' directory
• library/packages, namely 'shared', were moved to the 'packages' directory.
• The paths in the tsconfig files were adjusted to properly import the new mappings.
• 'shared' was renamed to '@packages/shared' to signal that it's a local import
• The 'shared' project does not need to be built before it can be used anymore. The contained typescript files can be used as is.
• Utility commands for joint building and running were added.
• The precommit hook for linting was fixed. It also sorts the imports. Note: we could also enable the 'linter' in the precommit hook for maximum gain, however currently we have too many lint issues in the 'api project which we need to fix first.

This structure is easily extensible, ie. once we start working on a new package (e.g. vortex-signer), we can put it into the 'packages' directory and easily import it everywhere.

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[ebma]

The ci is failing because we have too many lint issues. We should address them in a separate PR though.