Refactor and harden the Model Linker extension: normalize string quoting/formatting and improve logging and error responses across API routes. Make route registration more robust to missing PromptServer and dependencies. Add/expand download-related features: safer request parsing (including is_urn handling), CivitAI URN support & direct download URL resolution, popular/model-list/HuggingFace/CivitAI search fallbacks, improved header handling for HF/CivitAI, and better category/directory mapping. Improve downloader reliability and UX: folder_paths fallback, pre-initialize download progress entries, smoother speed calculation and CLI logging, cancellation cleanup on Windows, stronger exception handling, and consistent JSON responses from endpoints.