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/base.html

@@ -145,7 +145,7 @@
                                 <li>
                                     <a class="text-white hover:text-teal-500" href="{{ url_for('rounds.rounds_list') }}">View Rounds</a>
                                 </li>
-                                {% if current_user.is_admin() %}
+                                {% if current_user.is_admin %}
                                 <li class="group relative">
                                     <button class="peer flex items-center text-white hover:text-teal-500">
                                         <i class="fas fa-shield-alt mr-2"></i>Admin <i class="fas fa-chevron-down ml-1"></i>