Add tool result streaming

- Add AgentToolUpdateCallback type and optional onUpdate callback to AgentTool.execute()
- Add tool_execution_update event with toolCallId, toolName, args, partialResult
- Normalize tool_execution_end to always use AgentToolResult (no more string fallback)
- Bash tool streams truncated rolling buffer output during execution
- ToolExecutionComponent shows last N lines when collapsed (not first N)
- Interactive mode handles tool_execution_update events
- Update RPC docs and ai/agent READMEs

fixes #44

packages/agent/src/types.ts

@@ -95,4 +95,5 @@ export type AgentEvent =
 	| { type: "message_end"; message: AppMessage }
 	// Tool execution lifecycle
 	| { type: "tool_execution_start"; toolCallId: string; toolName: string; args: any }
+	| { type: "tool_execution_update"; toolCallId: string; toolName: string; args: any; partialResult: any }
 	| { type: "tool_execution_end"; toolCallId: string; toolName: string; result: any; isError: boolean };