PDA general maintenance (NTNet downloader rework) (#79741)

## About The Pull Request

I deleted the documentation file of ModPCs because it was barebones and
had no new information to give that autodoc couldn't. Just to make sure
this isn't a net-negative, I improved on much of the autodoc and
comments in general around ModPC code to help people understand easier
what's going on around it.
I also renamed vars that were too easily confused with other var names,
and reworked the ntnet downloader a little;
- it now has a search bar
- it now has more sections to scroll through, hopefully making it more
accurate and easy to find what you need.
- also organized the apps that were previously shoved in 'other'.
- i also upgraded it to a .tsx because why not

video demonstration


https://github.com/tgstation/tgstation/assets/53777086/cbba4c1c-b8a8-4ba4-8628-aea8389999fc

## Why It's Good For The Game

Adds in a lot of comments that were previously missing, clears up some
sources of confusion within ModPC code, and improves NTNet Downloader,
something I've procrastinated on doing for a very long time now.

## Changelog

🆑
qol: NTNet Downloader now has a search bar, and programs are now better
sorted.
/🆑

code/modules/modular_computers/computers/item/computer.dm

@@ -402,7 +402,7 @@
 		return
 
 	if(enabled)
-		. += active_program ? mutable_appearance(init_icon, active_program.program_icon_state) : mutable_appearance(init_icon, icon_state_menu)
+		. += active_program ? mutable_appearance(init_icon, active_program.program_open_overlay) : mutable_appearance(init_icon, icon_state_menu)
 	if(atom_integrity <= integrity_failure * max_integrity)
 		. += mutable_appearance(init_icon, "bsod")
 		. += mutable_appearance(init_icon, "broken")