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/process.py

@@ -1,16 +1,15 @@
 from flask import Blueprint, session, redirect, url_for, jsonify, request, current_app
+from flask_login import login_required
 import base64
 
 process_bp = Blueprint('process', __name__, url_prefix='/process')
 
 @process_bp.route('/base64', methods=['POST'])
+@login_required
 def base64_encode_data():
     """
     Return base64-encoded string from data provided in request body.
     """
-    if 'access_token' not in session:
-        return redirect(url_for('users.login'))  # Assuming 'users.login' is the correct endpoint
-    
     # Get binary data from request
     data = request.get_data()
     if not data: