v1.2.0 - Thinking Chain, Mermaid/KaTeX, Dark Mode, Multi-turn + Desktop App

🆕 New Features

• 🧠 Thinking chain display (collapsible reasoning process)
• 📊 Mermaid diagram rendering (flowcharts, sequence, class, ER)
• 📐 KaTeX math formula rendering (inline and block)
• 🌙 Dark mode support (auto-detect via prefers-color-scheme)
• 💬 Multi-turn conversation history (10-turn context window)
• 🔍 Project selector with search/filter
• 🏗️ Vite code splitting for faster load
• 🖥️ macOS desktop app (.dmg distributable)

🔧 Fixes

• Fix thinking SSE cross-chunk detection (pendingBuf accumulation)
• Fix Mermaid 11.x async API compatibility
• Fix Vite 8.x manualChunks function signature
• Fix image lazy loading

⚡ Infrastructure

• 16 DB performance indexes
• HikariCP pool optimization (max 20, min-idle 5)
• Gzip compression, Keep-alive timeout
• Auto-updater latest.json