fix: install.sh — sleep-safe, auto-display, fresh-machine install

- install.sh now has 8 steps:
  1) Detect arch, 2) Install deps, 3) Disable sleep/lock/screensaver,
  4) Detect display, 5) Setup dummy + force DUMMY0 primary,
  6) Start Xorg/Xvfb, 7) Download+install RustDesk (with apt fallback),
  8) Install systemd unit rustdesk-headless.service

- New systemd unit: rustdesk-headless.service
  * Forces DUMMY0 as primary via ExecStartPre (no monitor selection dialog)
  * Restart=always — survives any crash
  * Wants=display-manager.service — starts after graphical session

- Sleep-safe changes:
  * Mask sleep.target suspend.target hibernate.target hybrid-sleep.target
  * logind.conf: HandleLidSwitch=ignore, IdleAction=ignore
  * GNOME screensaver: gsettings lock-enabled false, idle-delay 0
  * X11: xset s off -dpms

- Fresh machine fixes:
  * dpkg --force-depends --force-confnew (installs even with missing deps)
  * apt-get install -f after dpkg (fixes broken deps)
  * Fallback to 'apt-get install rustdesk' from repo if .deb download fails
  * Added libva-drm2 libva-x11-2 (fresh systems often miss these)

- Output at end:
  * ID, Password, Display (:0 DUMMY0 primary), Sleep/Lock status
  * Monitor status via xrandr --listmonitors

Fixes #7

config/systemd/rustdesk-headless-inhibit.service

@@ -0,0 +1,18 @@
+[Unit]
+Description=Inhibit system sleep while RustDesk is active
+After=rustdesk-headless.service
+
+[Service]
+Type=simple
+ExecStart=/bin/bash -c '\
+    while true; do \
+        if pgrep -f "/usr/share/rustdesk/rustdesk --server" >/dev/null; then \
+            systemd-inhibit --what=sleep:idle:handle-lid-switch --who="RustDesk" --why="Remote access active" sleep 60; \
+        else \
+            sleep 5; \
+        fi; \
+    done'
+Restart=always
+
+[Install]
+WantedBy=multi-user.target

config/systemd/rustdesk-headless.service

@@ -0,0 +1,40 @@
+[Unit]
+Description=RustDesk Headless Server (auto-display, sleep-safe)
+After=display-manager.service graphical.target network.target
+Wants=display-manager.service
+
+[Service]
+Type=simple
+User=root
+Environment="DISPLAY=:0"
+Environment="XAUTHORITY=/root/.Xauthority"
+Environment="LIBVA_DRIVER_NAME=none"
+Environment="VDPAU_DRIVER=none"
+Environment="LIBGL_ALWAYS_SOFTWARE=1"
+Environment="LIBGL_ALWAYS_INDIRECT=1"
+
+# Force DUMMY0 primary before starting
+ExecStartPre=/bin/bash -c '\
+    for i in 1 2 3 4 5 6 7 8 9 10; do \
+        if xrandr >/dev/null 2>&1; then \
+            if xrandr | grep -q "^DUMMY0"; then \
+                xrandr --output DUMMY0 --mode "1920x1080" --primary 2>/dev/null || true; \
+                exit 0; \
+            fi; \
+        fi; \
+        sleep 1; \
+    done'
+
+ExecStart=/usr/share/rustdesk/rustdesk --server
+ExecStartPost=/bin/bash -c 'echo "RustDesk started, ID: $(/usr/share/rustdesk/rustdesk --get-id 2>/dev/null || echo unknown)" >> /tmp/rustdesk-server.log'
+
+Restart=always
+RestartSec=10
+StartLimitInterval=60
+StartLimitBurst=3
+
+# Prevent system sleep while RustDesk is active
+ExecStopPost=/bin/systemctl start --no-block rustdesk-headless-inhibit.service
+
+[Install]
+WantedBy=multi-user.target