MCP tools are now prefixed with their server name (e.g., vigil-harbor:memory_status)
to prevent collisions between tools from different MCP servers and built-in tools.
Adds SSE and StreamableHTTP transport support alongside existing stdio, enabling
connection to remote MCP servers via URL-based config with optional custom headers
and env var substitution. Includes config validation, session lifecycle management,
and 5 new tests for HTTP config edge cases.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>