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/core.py

@@ -302,7 +302,10 @@ def serve_user_audio(filepath):
     """
     Serve user custom audio files from the data directory
     """
-    if '..' in filepath:
+    # Resolve the real path to prevent path traversal attacks
+    base_dir = os.path.realpath('/data')
+    requested_path = os.path.realpath(os.path.join('/data', filepath))
+    if not requested_path.startswith(base_dir + os.sep) and requested_path != base_dir:
         abort(404)
         
     if 'custommp3/' in filepath: