Initial commit: xenforo-dl reimplementation

Add complete TypeScript project for a XenForo forum downloader. Includes CLI (parsing, validation, interactive prompts), core downloader (thread/forum/generic processing, attachment download, continuation support), parsers/entities/templates, fetcher and logging utilities, and helper utils. Also add package.json with build/bundle scripts, bin wrappers, README, ESLint/TS configs, and npm ignore/gitignore files to support development and packaging.