v1.3.0: Model browser & tab awareness

What changed

• HuggingFace model browser — search, preview, and download GGUF models directly from Settings
• Mood ring for session tabs — color-coded glow shows error/warning activity at a glance
• Duplicate Session from tab context menu — quickly clone any connection
• HEX mode badge in status bar with pulsing indicator
• Simplified embedding model setup — Nomic Embed auto-bundles with LLM downloads
• Fixed false activity indicators on inactive tabs caused by split ANSI sequences
• Free tier RAG document limit now enforced on all import paths
• GPU detection fix for Vulkan builds on NVIDIA hardware