Switch desktop environment from Hyprland to Pantheon

Configures Pantheon (LightDM + gala) for daily use on this ASUS TUF
Gaming A15 (FA507NU), and drops everything that only existed to serve
the previous Hyprland/Quickshell setup:

- desktop.nix: services.desktopManager.pantheon instead of
  programs.hyprland + greetd; comfy laptop touchpad defaults.
- drivers.nix: NVIDIA PRIME render offload between the AMD Radeon 680M
  (drives the panel) and the RTX 4050 Max-Q (offload-only), using this
  machine's real PCI bus IDs; asusd/supergfxd for ASUS-specific laptop
  control.
- apps.nix / scripts.nix: removed Hyprland/Quickshell-only packages and
  scripts (kitty, rofi, quickshell, mako, hyprlock, hyprpaper/mpvpaper,
  the Quickshell theme-picker scripts, cursor/wallpaper/display
  helpers) — Pantheon ships its own Files/Terminal/Screenshot/
  notifications/theming natively. Kept the DE-agnostic scripts (vault
  toggle, metadata stripping, brightness control, Wi-Fi hotspot,
  telemetry, weather).
- theme.nix and default-apps.nix deleted entirely — Pantheon owns
  GTK/icon theming itself, no more live dconf/CSS generation pipeline
  needed.
- Deleted hyprland/ and dotfiles/ (kitty, mako, quickshell, rofi).

Verified with `nixos-rebuild build`.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01RpiovBQL6k5MTDMN3Ln9nL

modules/scripts/brightness-ctl.sh

@@ -0,0 +1,56 @@
+#!/usr/bin/env bash
+# Brightness control abstraction: prefers the kernel backlight class (laptop
+# panels, via brightnessctl); falls back to DDC/CI over I2C (external
+# monitors, via ddcutil) when no backlight device exists. Keeps the rest of
+# the config (Quickshell's brightness popup) hardware-agnostic.
+set -euo pipefail
+
+has_backlight() {
+    [ -n "$(ls -A /sys/class/backlight 2>/dev/null)" ]
+}
+
+case "${1:-get}" in
+    get)
+        if has_backlight; then
+            brightnessctl -m | cut -d, -f4 | tr -d '%'
+        else
+            ddcutil getvcp 10 --brief 2>/dev/null | awk '{print $4}'
+        fi
+        ;;
+    set)
+        pct="${2:?usage: brightness-ctl set <0-100>}"
+        if has_backlight; then
+            brightnessctl set "${pct}%" > /dev/null
+        else
+            ddcutil setvcp 10 "$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>|up [step]|down [step]]" >&2
+        exit 1
+        ;;
+esac