ONNX bundling and companion tool polish

Work picked back up across three tracks after the quiet period. The main app bundled ONNX Runtime via Tauri resources with a cross-platform setup script, documented streaming patterns after the Channel migration, and resolved four review findings around OnceLock, fatal init, AtomicBool, and an isGenerating desync. GIMP helper added macros and fast paths alongside refined LLM planning and UI work. LibreOffice integration continued moving forward with app and documentation improvements.