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

lib/system/user.sh

@@ -0,0 +1,66 @@
+#!/bin/bash
+
+# Copyright 2026 Logan Fick
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     https://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+# user.sh - User account management
+#
+# Creates the primary user account with wheel group membership.
+
+# Prompt for username
+# Sets:
+#   USERNAME - the entered username
+prompt_username() {
+    local username
+
+    while true; do
+        print "Please enter the username you'd like to use for your account:"
+        read -r username
+
+        if validate_username "$username"; then
+            USERNAME="$username"
+            return 0
+        fi
+
+        print "Please try again."
+    done
+}
+
+# Create a user account
+# Arguments:
+#   $1 - username
+create_user() {
+    local username="$1"
+
+    chroot_run useradd -m -G wheel "$username"
+}
+
+# Set password for a user
+# Arguments:
+#   $1 - username
+set_user_password() {
+    local username="$1"
+
+    print "Please set the password for your new account."
+    chroot_run passwd "$username"
+}
+
+# Full user setup
+# Sets:
+#   USERNAME - the created username
+setup_user() {
+    prompt_username
+    create_user "$USERNAME"
+    set_user_password "$USERNAME"
+}