- Update @mariozechner/pi-agent-core, pi-ai, pi-coding-agent, pi-tui to 0.51.0
- Delete src/types/pi-coding-agent.d.ts (declared additionalExtensionPaths which SDK never supported)
- Fix ToolDefinition.execute signature (parameter order changed in 0.51.0)
- Remove dead additionalExtensionPaths from createAgentSession calls