docs: Add comprehensive platform overview

Comprehensive overview document covering:
- Production-ready features and capabilities
- Compliance standards (OAuth 2.1, OIDC, security grade A-)
- Cost comparison vs Clerk/Auth0/Supabase (/bin/zsh vs ,500/month)
- Native MCP server integration patterns
- Agent-to-agent (A2A) authentication patterns
- Future roadmap (near-term and long-term)
- Getting started guides for apps, MCP servers, and AI agents

Key highlights:
- Full multi-tenant architecture with zero cost
- Native support for MCP servers and AI agents
- 5 detailed A2A authentication patterns
- Enterprise-grade security (A- rating)
- Production-ready with comprehensive docs

Target audiences: Developers, DevOps, CTOs, AI agent builders

🤖 Generated with Claude Code
https://claude.com/claude-code

Co-Authored-By: Claude <[email protected]>

Author: mjunaidca