dsh-config-migrate v1.0.0

DeepSeek Harness config migration plugin.

• Cross-platform (Windows/macOS/Linux)
• One-click export/import of DSH_HOME config
• Credential encryption (AES-256-GCM)
• External plugin migration (binary assets + junction/symlink rebuild)
• v1/v2 bundle compat, dry-run preview, only-missing mode
• 27 unit tests, 3-platform CI