fix: resolve logical errors, bugs, and security issues across codebase

- Fix is_admin() method shadowing is_admin database column in User model
- Fix check_password() crash when password_hash is None (OAuth-only users)
- Fix SystemSetting.all_settings() formatting error (missing newline)
- Fix MAIL_PORT returning string instead of int in config
- Fix AUTOMATION_TOKEN config formatting (missing newline before comment)
- Fix path traversal vulnerability in serve_user_audio using realpath validation
- Fix weak auth in process.py, replace session check with @login_required
- Fix int() crash on non-numeric priority in import_songs.py
- Add timeout to SMTP connection in email_helper.py
- Add timeouts to external API requests in metadata.py and spotify_helper.py
- Fix security tests to properly reload config module
- Fix metadata test mock data key mismatch (preview_url -> spotify_preview_url)
- Add skip decorator to integration test requiring live API credentials

Co-authored-by: christianlouis <361235+christianlouis@users.noreply.github.com>

musicround/templates/users/profile.html

@@ -38,7 +38,7 @@
                     <div>
                         <p class="text-sm text-gray-600">Admin Status</p>
                         <p class="font-medium">
-                            {% if current_user.is_admin() %}
+                            {% if current_user.is_admin %}
                                 <span class="text-green-600">Administrator</span>
                                 <a href="{{ url_for('admin.index') }}" class="ml-2 text-xs text-blue-600 hover:underline">
                                     Admin Dashboard
@@ -73,7 +73,7 @@
             </div>
             
             <!-- Spotify Connection Debug - Only for Admins -->
-            {% if current_user.is_admin() %}
+            {% if current_user.is_admin %}
             <div class="mt-6 p-4 border border-gray-300 rounded-lg bg-gray-50">
                 <div class="flex items-center justify-between mb-3">
                     <h3 class="text-lg font-semibold text-navy-700">Spotify Connection Debug</h3>
@@ -144,7 +144,7 @@
             <h3 class="text-lg font-semibold mb-4 text-navy-700">Connected Services</h3>
             
             <!-- Spotify Connection - Only shown for admins -->
-            {% if current_user.is_admin() %}
+            {% if current_user.is_admin %}
             <div class="bg-gray-50 p-4 rounded-lg mb-4 shadow-sm">
                 <div class="flex items-center mb-3">
                     <i class="fab fa-spotify text-[#1DB954] text-2xl mr-3"></i>
@@ -269,7 +269,7 @@
 </div>
 
 <!-- Spotify Debug Modal - Only for Admins -->
-{% if current_user.is_admin() %}
+{% if current_user.is_admin %}
 <div id="spotifyDebugModal" class="fixed inset-0 bg-black bg-opacity-50 flex items-center justify-center z-50 hidden">
     <div class="bg-white rounded-lg shadow-lg w-full max-w-2xl max-h-[80vh] overflow-y-auto">
         <div class="p-6">
@@ -760,7 +760,7 @@
 {% endblock %}
 
 {% block scripts %}
-{% if current_user.is_admin() %}
+{% if current_user.is_admin %}
 <script>
     document.addEventListener('DOMContentLoaded', function() {
         const modal = document.getElementById('spotifyDebugModal');