chore(dots): Remove unused programs

I have stopped using aerc, guix, khal, khard and vdirsyncer, as I
primarily use macOS for work nowdays.

This has also meant that I've generally transitioned from using
terminal-based tools to using GUI tools that I can wrap in my window
manager environment.

chore(nvim): Remove obsidian plugin

This was not being used at all

chore(nixpkgs): Swap from kitty to alacritty

I always preferred alacritty, but there was a bug that meant I couldn't
use my keybinds for tmux and neovim. This bug has now fortunately been
resolved, so I can go back to alacritty :)

feat(alacritty): Migrate to TOML configuration files

chore(nvim/status): Change modified indicator and update lsp function

feat(tmux): Ensure terminal-features are set to RGB

This helps ensure correct display for neovim

feat(nix): Swap to using lix instead of nix

chore(nixpkgs): Update yabai to v7.1.5

feat(nixpkgs): Reorganise installed programs

feat(nvim,kitty,tmux): Have copy and paste work for remote SSH sessions

This uses OSC52. I previously failed to get this working, but these
configuration changes ended up having it working for me

feat(nvim): Use OSC52 to copy clipboard if in an SSH session

This should make some of my remote work significantly easier

chore(nixpkgs): Remove unused configuration and rename computer to `apollo`

It was originally apollo and then my work remote renamed it for me :(

chore(nixpkgs): Abstract out flake.nix from darwin directory

feat(nixpkgs): Ensure that nix flakes would work for all systems

feat(nixpkgs,nvim): Use nixd instead of rnix for nix LSP

rnix is now deprecated, and nixd is suggested as its replacement

chore(nixpkgs): Remove currently unused applications

I'm not using any of these in my current workflow, so I'm removing them

feat(nixpkgs): Add flake file

feat(nixpkgs): Upgrade to stateVersion 5, allow experimental-features

chore(yabai): Upgrade to 7.1.4

fix(yabai): Ensure that System Settings doesn't get managed

This started to fail because the name of the application changed in
Ventura. I was too lazy to fix it before :)