fix: Fix setup bugs, add SteamOS desktop look and LED driver, split into modules

- Fix session switching: sync bridge only edits [Autologin], sync service
  no longer hits systemd's start limit, re-runs don't duplicate settings
- Make the Return to Gaming Mode shortcut work without a password prompt
- Steam desktop autostart only runs in Plasma, not inside gamescope
- Vapor theme: fix install path, wallpaper, icon and color scheme; take
  over Valve's SteamOS defaults, GTK theme, panel layout and dark mode;
  always fetch the newest steamdeck-kde-presets with checksum verification
- Steam Machine: install kernel headers and build/load the leds-valve
  driver reliably; ask before installing OpenRGB
- Split the script into lib/ modules per responsibility
- Rewrite README for end users with a technical details section; add
  AGENTS.md

lib/led-driver.sh

@@ -0,0 +1,113 @@
+#!/bin/bash
+# Valve Fremont (Steam Machine) front LED bar driver.
+# Sourced by setup-gamescope-boot.sh; not meant to be run on its own.
+
+detect_valve_fremont() {
+    # Valve Steam Machine (Fremont) boards. The leds-valve driver's own DMI
+    # table also matches the OEM/F7F strings some early units report, so
+    # accept both -- otherwise we'd skip hardware the driver supports.
+    local vendor product
+    vendor="$(cat /sys/class/dmi/id/sys_vendor 2>/dev/null || true)"
+    product="$(cat /sys/class/dmi/id/product_name 2>/dev/null || true)"
+    [[ "$vendor" == "Valve" && "$product" == "Fremont" ]] ||
+        [[ "$vendor" == "OEM" && "$product" == "F7F" ]]
+}
+
+install_kernel_headers() {
+    # DKMS can only build leds-valve against kernels whose headers are
+    # installed. CachyOS ships several kernels (linux-cachyos, -lts, -bore,
+    # ...); install the matching -headers package for every one present.
+    local -a kernels headers=()
+    mapfile -t kernels < <(pacman -Qqo /usr/lib/modules/*/pkgbase 2>/dev/null | sort -u)
+    local k
+    for k in "${kernels[@]}"; do
+        pacman -Si "${k}-headers" >/dev/null 2>&1 && headers+=("${k}-headers")
+    done
+    if [[ ${#headers[@]} -eq 0 ]]; then
+        warn "Couldn't work out which kernel headers package you need."
+        warn "Install the -headers package for your kernel (e.g. linux-cachyos-headers) yourself."
+        return 1
+    fi
+    info "Making sure kernel headers are installed: ${headers[*]}"
+    sudo pacman -S --needed --noconfirm "${headers[@]}"
+}
+
+install_valve_led_driver() {
+    # Installs the leds-valve DKMS driver from the AUR so the front LED
+    # bar is exposed under /sys/class/leds/valve-leds[N].
+    local aur_helper
+    aur_helper="$(find_aur_helper)"
+    if [[ -z "$aur_helper" ]]; then
+        warn "No AUR helper available - can't install leds-valve-dkms-git."
+        warn "Install one yourself, then run: yay -S leds-valve-dkms-git"
+        return 1
+    fi
+
+    local -a flags
+    read -ra flags <<< "$(aur_noninteractive_flags "$aur_helper")"
+
+    # Headers first: without them the package installs fine but DKMS
+    # silently builds nothing, so modprobe later finds no module.
+    install_kernel_headers || return 1
+
+    if ! pacman -Qi leds-valve-dkms-git >/dev/null 2>&1; then
+        info "Installing leds-valve-dkms-git from the AUR via $aur_helper (non-interactive)..."
+        if ! "$aur_helper" -S "${flags[@]}" leds-valve-dkms-git; then
+            err "Installing leds-valve-dkms-git failed."
+            return 1
+        fi
+    else
+        ok "leds-valve-dkms-git already installed."
+    fi
+
+    # Build for the running kernel explicitly. The upstream Makefile uses
+    # `uname -r` rather than DKMS's target kernel, so building for the
+    # running kernel is the one case that reliably works.
+    local kver
+    kver="$(uname -r)"
+    if ! dkms status -k "$kver" leds-valve-dkms 2>/dev/null | grep -q installed; then
+        info "Building leds-valve for running kernel $kver..."
+        if ! sudo dkms install leds-valve-dkms/0.1 -k "$kver"; then
+            err "DKMS build failed. See the build log:"
+            err "  /var/lib/dkms/leds-valve-dkms/0.1/build/make.log"
+            return 1
+        fi
+    fi
+
+    # Load now, and on every boot.
+    echo leds-valve | sudo tee /etc/modules-load.d/leds-valve.conf >/dev/null
+
+    info "Loading the leds-valve kernel module..."
+    if sudo modprobe leds-valve; then
+        ok "Module loaded."
+    else
+        warn "modprobe leds-valve failed. Kernel messages:"
+        sudo dmesg | grep -i 'valve' | tail -n 10
+    fi
+
+    if compgen -G "/sys/class/leds/valve-leds*" >/dev/null; then
+        ok "LED bar nodes detected: $(cd /sys/class/leds && echo valve-leds*)"
+    else
+        warn "No valve-leds nodes under /sys/class/leds/ yet. Reboot, then check with:"
+        warn "  ls /sys/class/leds/ | grep valve ; sudo dmesg | grep -i valve"
+    fi
+
+    echo
+    info "Steam only pushes download progress to the LED bar in real SteamOS Game Mode."
+    if ask_yn "Also install the experimental OpenRGB build (openrgb-git), which can drive the LED bar?" n; then
+        "$aur_helper" -S "${flags[@]}" openrgb-git &&
+            ok "openrgb-git installed. Launch OpenRGB to detect and configure the front panel."
+    fi
+}
+
+setup_led_driver() {
+    # Step 8c: only on Fremont hardware, and only if the user wants it.
+    if detect_valve_fremont; then
+        info "Detected Valve Fremont hardware (Steam Machine)."
+        if ask_yn "Set up the front-panel LED bar driver (leds-valve) so it isn't stuck dark/breathing?" y; then
+            ensure_aur_helper || warn "Couldn't set up an AUR helper automatically. You can install one yourself later and run: yay -S leds-valve-dkms-git"
+            install_valve_led_driver || warn "LED driver setup ran into a problem - see errors above. Your gamescope boot setup above is unaffected."
+        fi
+        echo
+    fi
+}