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/waybar/dev.sh

@@ -0,0 +1,40 @@
+#!/usr/bin/env nix-shell
+#!nix-shell -i bash -p inotify-tools waybar mako swaynotificationcenter libnotify pavucontrol
+
+# This script will watch waybar.nix and compile it to /tmp/waybar.json.  Offers
+# a much tighter feedback loop than that offered by the Nix module.
+
+# Inotify will sometimes double-fire events.  We avoid unnecessary recompilation
+# by putting a cooldown on builds.
+last_build=0
+waybar_pid=""
+
+update () {
+  last_build="$(date +%s)"
+
+  if [ ! -z "$waybar_pid" ]; then
+      kill "$waybar_pid"
+      echo >&2 "Killed waybar..."
+      waybar_pid=""
+  fi
+
+  echo >&2 "Building waybar.json..."
+  nix eval --impure --json --expr "import ./waybar.nix {}" \
+      > /tmp/waybar.json \
+      && echo >&2 "Built waybar.json!"
+  waybar -c waybar.json -b sydbar -s waybar.css 2>&1 >/dev/null &
+  waybar_pid=$!
+  echo >&2 "Started Waybar [$waybar_pid]" 
+}
+
+update
+
+inotifywait -me modify waybar.nix waybar.css cycle_notifications.clj |
+    while read _ _ file_name; do
+        ct="$(date +%s)"
+        if (( ct - last_build < 1 )); then
+            echo >&2 "Ignoring event (on cooldown)"
+        else
+            update
+        fi
+    done