alex2

feat: web chat interface, plugin marketplace, and README overhaul

• Add live AI chat page to dashboard (POST /api/chat with tool call chips,
  typing indicator, provider badge, clear history)
• Add Plugin Marketplace page with category filters, enable/disable toggles,
  and auth requirement labels
• Wire pre-initialized Conductor into dashboard server for zero-latency chat
• Add clearHistory() to DatabaseManager
• Add /api/chat, /api/chat/history, /api/marketplace endpoints to server
• Overhaul README: badge row, 60-second quickstart, architecture diagram,
  “5 things that will impress you” section, real example prompts