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/routes/db_admin.py

@@ -18,7 +18,7 @@ def admin_required(view_func):
         if not current_user.is_authenticated:
             return redirect(url_for('users.login'))
         
-        if not current_user.is_admin():
+        if not current_user.is_admin:
             flash('Admin access required.', 'danger')
             return redirect(url_for('core.index'))
             
@@ -37,7 +37,7 @@ def raw_db_access():
 # Base model view with authentication
 class AuthModelView(ModelView):
     def is_accessible(self):
-        return current_user.is_authenticated and current_user.is_admin()
+        return current_user.is_authenticated and current_user.is_admin
     
     def inaccessible_callback(self, name, **kwargs):
         if not current_user.is_authenticated: