Implemented OAuth 2.0 Authorization Code Flow with PKCE support

ADDED -Full OAuth 2.0 Authorization Code Flow with PKCE (RFC 7636)
ADDED - Dynamic client registration endpoint (RFC 7591)
ADDED - Custom authorization form for seamless OAuth flow without WordPress login
ADDED -OAuth discovery endpoint (/.well-known/oauth-authorization-server)
ADDED - Support for claude.ai web version authentication
ENHANCED - JWT authentication to accept tokens with or without Bearer prefix
IMPROVED - Claude Code compatibility with OAuth-compliant error responses
IMPROVED - Token endpoint returns OAuth-standard response format (access_token, token_type)
ADDED - Activation/deactivation hooks for automatic OAuth discovery file management
CHANGED - SECURITY: PKCE code challenge methods supported (S256, plain)
CHANGED - COMPATIBILITY: Works with Claude Code, Claude.ai web, and any MCP client supporting OAuth 2.0