feat: Add host sydpc

My, this is a lot TwT.  Much work was batched as part of the transition from
guix-rebound to nixos-testbed/sydpc.

- Discord/Vesktop module & config.
- Syncthing setup.
- Assorted Emacs changes.
- Waybar config.
- Niri config.
- Steam config.
- Some MPD.
- Stylix config.
- Files/Impermanence things.
- Enable Ghostty.
- God knows what else.

modules/nixos/niri.nix

@@ -0,0 +1,13 @@
+{ config, lib, pkgs, ... }:
+
+let
+  cfg = config.sydnix.niri;
+in {
+  options.sydnix.niri.enable =
+    lib.mkEnableOption "Niri";
+
+  config = lib.mkIf cfg.enable {
+    programs.niri.enable = true;
+  };
+}
+

modules/nixos/steam.nix

@@ -0,0 +1,32 @@
+{ config, pkgs, lib, inputs, system, ... }:
+
+let cfg = config.sydnix.steam;
+in {
+  options.sydnix.steam = {
+    enable = lib.mkEnableOption "Steam";
+  };
+
+  config = lib.mkIf cfg.enable {
+    programs.steam = {
+      enable = true;
+      remotePlay.openFirewall = true;
+      dedicatedServer.openFirewall = true;
+      gamescopeSession.enable = true;
+      extraPackages = with pkgs; [
+        mono gtk3 gtk3-x11 libgdiplus zlib
+      ];
+    };
+
+    programs.gamemode = {
+      enable = true;
+      enableRenice = true;
+    };
+
+    # This fixes the "glXChooseVisual failed" bug, see:
+    # https://github.com/NixOS/nixpkgs/issues/47932.
+    hardware.graphics = {
+      enable = true;
+      enable32Bit = true;
+    };
+  };
+}

modules/nixos/stylix.nix

@@ -0,0 +1,35 @@
+
+{ config, lib, pkgs, ... }:
+
+let
+  cfg = config.sydnix.stylix;
+in {
+  options.sydnix.stylix.enable =
+    lib.mkEnableOption "Stylix";
+
+  config = lib.mkIf cfg.enable {
+    stylix = {
+      enable = true;
+      base16Scheme = "${pkgs.base16-schemes}/share/themes/kanagawa.yaml";
+      image = ./stylix/kanagawa.jpg;
+      # fonts = {
+      #   serif = {
+      #     package = pkgs.ibm-plex;
+      #     name = "IBM Plex";
+      #   };
+      #   sansSerif = {
+      #     package = pkgs.dejavu_fonts;
+      #     name = "DejaVu Sans";
+      #   };
+      #   monospace = {
+      #     package = pkgs.nerd-fonts.victor-mono;
+      #     name = "VictorMono";
+      #   };
+      #   emoji = {
+      #     package = pkgs.twemoji-color-font;
+      #     name = "Noto Color Emoji";
+      #   };
+      # };
+    };
+  };
+}