Schematic Browser GUI

### The Problem

We have quite a few schematics on our server.
The flattening of subdirectories in particular makes it near impossible to navigate these.


### A Solution

Litematica does a great job at presenting schematics - however this won't work on a server.


Ideally the server would send the entire schematic tree to the player (just directories and file names, not their contents) such that the player can browse at their leisure.

### Alternatives

Alternatively, adding directory support to the '//schem list' command would already improve the user experience significantly.

For example '//schem list DinoSpear' may generate this output
```
---------- Available Schematics ----------
[D] \1.10\
[D] \1.12\
[D] \1.15\
[D] \1.7\
[L] 0,5ttest.schematic
[L] 1.schematic
[L] 2,1.schematic
```
Clicking on `[D]` would list the contents of that directory.

However, I believe that this alternative is not preferable, since the '//schem list' command is already unresponsive and this would likely amplify the problem.

### Anything Else?

_No response_