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/home/users/crumb/discord.nix

@@ -0,0 +1,33 @@
+{ config, lib, pkgs, ... }:
+
+let cfg = config.sydnix.users.crumb.discord;
+in {
+  options.sydnix.users.crumb.discord = {
+    enable = lib.mkEnableOption "Discord";
+  };
+
+  config = lib.mkIf cfg.enable {
+    sydnix.discord.enable = true;
+
+    programs.nixcord = {
+      config = {
+        themeLinks = [
+          # Compact++ (Default) — Themes Discord to look more like a typical IRC
+          # client.
+          "https://gitlab.com/api/v4/projects/52800868/snippets/3628352/files/main/compactplusplus-default.theme.css/raw"
+        ];
+        plugins = {
+          ircColors.enable = true;
+        };
+      };
+      vesktop = {
+        state.firstLaunch = false;
+        settings = {
+          discordBranch = "stable";
+          minimizeToTray = false;
+          arRPC = true;
+        };
+      };
+    };
+  };
+}