refactor(api): rename scan_frequency_minutes to scan_poll_interval_seconds

- Update API field from scan_frequency_minutes to scan_poll_interval_seconds
- Update database schema default value key
- Update Bruno API collection requests and documentation
- Update OpenAPI documentation examples and field descriptions

database/schema/schema.sql

@@ -43,7 +43,7 @@ CREATE TABLE IF NOT EXISTS system_settings (
 
 -- Insert default system settings
 INSERT INTO system_settings (setting_key, setting_value, description) VALUES
-('scan_frequency_minutes', '60', 'How often to scan all libraries in minutes'),
+('scan_poll_interval_seconds', '60', 'How often to scan all libraries in minutes'),
 ('auto_scan_enabled', 'true', 'Whether auto-scanning is enabled system-wide')
 ON CONFLICT (setting_key) DO NOTHING;