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Just removing some unused/unnecessary scripts and `IS_BETA` env variable
+ the associated code (we don't use this in the OS version of Actual).

Last one before I add the actual linter rules!

Depends on https://github.com/actualbudget/docs/pull/202.

Part 1 of the conversion. Mostly renaming js to ts and making sure
things make still sense. Added also handy TS ESLint rules.

In order to support the various .web/.electron/... I ended up adopting
`index.d.ts` as pattern to share type definition. Let me know if that
makes sense for you too. Right now the function type definition is
duplicated, but the solution will be importing from `index.d.ts` and
using `const fn: FnDef = () => ...` that way we can keep all variants in
sync from a single type file.

Such rewrite however is better done in another PR otherwise we risk
confusing git and loosing history (rename + too many changes). Another
thing that might do in the next PR is convert all files to ESModules, as
things get confusing between CJS exports, ESM default/named and TS adds
extra complains.

I'm not sure if this is something you want but it was a simple change so
I figured I might as well contribute it. This PR allows the user to
upload `.blob` files that they may have gotten from server's
`user-files/` folder. This can be useful if the user didn't export the
file but has server backups.

---------

Co-authored-by: Jed Fox <git@jedfox.com>

* Make it easier to build the bundle.api.js for the API

* Remove budgetId parameter, move config to top level of API

* that’s a breaking change

* Add support for signing into the server in init()

* Add api.downloadBudget(syncId, { password }) method

* Fix lint errors

* Refactor: extract out getSyncError

* api/download-budget: sync if possible instead of downloading

* Don’t bother with fetching remote files and installing key if the file is local

* *groupId

* FIx lint issues

* Remove extra close+reopen

* Refactor out duplicate load-budget logic

* Trailing commas