Json Sync

### Describe your improvement idea or feature request

Hey guys! This is awesome! Good to see a nice mobile app under development for TW.

I like to rely on SyncThing for a lot of my file syncing, which works great for text files. The task server works well but it's a dependency I shouldn't need with TW's [json export](https://taskwarrior.org/docs/3rd-party/) (which is apparently the recommended 3rd party integration mechanism). What would it take to support json as a sync option?

### How would you like to see it implemented?

1. Select sync option "json file"
2. Select file/dir

### Put here any screenshots or videos (optional)

_No response_

### How can we contact you (optional)

_No response_

### Would you like to work on this issue?

None

### By submitting this issue, I have confirmed that:

- [X] I have starred the repo ⭐ and watched 👀 it on GitHub and followed the contribution guidelines.

まず、既存の同期オプションと、issue にリンクされている Taskwarrior JSON エクスポートのドキュメントを確認します。同期ソースとファイルまたはディレクトリがどのように選択されるかを追跡し、その後、タスクサーバーなしで JSON ファイルのオプションを選択して使用できることを確認します。

索引モデルが issue の本文から書いたものです。