Refactored installer into modular library structure with improved error handling and logging.

The changes include:
- Split monolithic script into lib/, config/, profiles/, and files/ directories
- Added error handling with cleanup on failure
- Added installation logging to /var/log/arch-install.log
- Added username validation

files/etc/systemd/network/50-default-wlan.network

@@ -0,0 +1,19 @@
+[Match]
+Type=wlan
+WLANInterfaceType=station
+SSID=*
+
+[Link]
+RequiredForOnline=routable
+
+[Network]
+DHCP=yes
+IPv6AcceptRA=yes
+IgnoreCarrierLoss=3s
+EmitLLDP=yes
+
+[DHCPv4]
+RouteMetric=200
+
+[IPv6AcceptRA]
+RouteMetric=200