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/helpers/email_helper.py

@@ -82,7 +82,7 @@ def send_email(recipient, subject, body_text, attachments=None):
 
     try:
         current_app.logger.info(f"Attempting to send email to {recipient} via {mail_host}:{mail_port}")
-        with smtplib.SMTP(mail_host, mail_port) as server:
+        with smtplib.SMTP(mail_host, mail_port, timeout=30) as server:
             server.starttls()
             current_app.logger.debug("STARTTLS established")
             server.login(mail_username, mail_password)