dsh-fixed-new-session-model: Fix Default Model and Agent Presets for New Sessions

The DeepSeek Harness plugin addresses configuration inconsistencies caused by temporary in-session model switches that override global settings. It provides stable global default model and Agent presets, supports independent binding per workspace, and automatically applies configurations to new or empty sessions. With a native settings interface and field inheritance support, it also ensures high security by neither reading nor transmitting API keys. Users can install and configure it via commands to maintain the consistency and stability of DSH session settings.