docs: Add comprehensive API Reference page (210+ endpoints)
Covers all TITAN v1.1.1 gateway endpoints organized by category:
Core, Sessions, Chat, Models, Config, Skills, Marketplace, Personas,
Tools, Channels, Providers, VRAM, MCP, Agents, Mesh, Teams RBAC,
Goals, Recipes, Plugins, Autopilot, Daemon, Cron, Command Post,
Wakeup, Voice, Voice Cloning, NVIDIA Health, Training,
Autoresearch, Files, Audit, Browser, Activity, Memory Graph,
Profile, Learning, Soul, Google OAuth, Tunnel, Costs/Usage,
Update, Metrics, Onboarding, and Data Management.
Co-Authored-By: Paperclip <noreply@paperclip.ing>