Add on-screen display, sidebar keybinds, function keys, gh package

- Add Osd.qml: themed top-center popup for volume/mic/brightness/media
  changes. Volume and mic react directly to Pipewire so they fire for
  any change, not just our own keybinds; brightness is notified
  explicitly (no live service exists for DDC/CI writes); media is
  driven by two playerctl --follow watchers (status + metadata) so
  track changes, pause/resume, and stop all show correctly without
  double-firing
- Add Super+Shift+Z/X to toggle the Left/RightBar sidebars, via a new
  Quickshell IpcHandler wired to the same expand/collapse logic as the
  BottomBar arrows
- Add function-key binds for volume up/down/mute, mic mute, brightness
  up/down, and media play/pause/stop/next/prev (wpctl/playerctl);
  extend brightness-ctl with relative up/down steps for both the
  backlight and DDC/CI paths
- Add gh and playerctl to packages

modules/scripts/brightness-ctl.sh

@@ -25,8 +25,32 @@ case "${1:-get}" in
             ddcutil setvcp 10 "$pct" > /dev/null
         fi
         ;;
+    up|down)
+        # brightnessctl takes a relative step directly, but ddcutil's
+        # setvcp only takes an absolute value — so the DDC/CI path (this
+        # machine's AOC 27G2G8 has no backlight device, so it always takes
+        # this path) has to read the current level and clamp the step
+        # itself.
+        step="${2:-5}"
+        if has_backlight; then
+            if [ "$1" = "up" ]; then
+                brightnessctl set "+${step}%" > /dev/null
+            else
+                brightnessctl set "${step}%-" > /dev/null
+            fi
+        else
+            cur=$(ddcutil getvcp 10 --brief 2>/dev/null | awk '{print $4}')
+            cur="${cur:-50}"
+            if [ "$1" = "up" ]; then
+                new=$(( cur + step > 100 ? 100 : cur + step ))
+            else
+                new=$(( cur - step < 0 ? 0 : cur - step ))
+            fi
+            ddcutil setvcp 10 "$new" > /dev/null
+        fi
+        ;;
     *)
-        echo "usage: brightness-ctl [get|set <0-100>]" >&2
+        echo "usage: brightness-ctl [get|set <0-100>|up [step]|down [step]]" >&2
         exit 1
         ;;
 esac