feat: add gamification support with Habitica integration

[byq77]

Closes #1384

Description: TODO

[st3v3nmw]

Thanks for the proposal and the effort you put into this.

I'm wary of merging it though, since it adds a hard dependency on a third-party API, which means maintenance burden every time Habitica changes something on their end.

The underlying motivation makes sense to me, but I'd rather address it natively, think streak tracking and a review heatmap along the lines of what Anki does. That keeps everything self-contained.

I did briefly consider whether a plugin extension system could be the right answer here, but given that this is already an Obsidian plugin, I'm not sure that's a rabbit hole worth going down.