Add hooks system with pi.send() for external message injection

- Hook discovery from ~/.pi/agent/hooks/, .pi/hooks/, --hook flag
- Events: session_start, session_switch, agent_start/end, turn_start/end, tool_call, tool_result, branch
- tool_call can block execution, tool_result can modify results
- pi.send(text, attachments?) to inject messages from external sources
- UI primitives: ctx.ui.select/confirm/input/notify
- Context: ctx.exec(), ctx.cwd, ctx.sessionFile, ctx.hasUI
- Docs shipped with npm package and binary builds
- System prompt references docs folder

packages/coding-agent/src/index.ts

@@ -9,6 +9,12 @@ export type {
 	HookEventContext,
 	HookFactory,
 	HookUIContext,
+	SessionStartEvent,
+	SessionSwitchEvent,
+	ToolCallEvent,
+	ToolCallEventResult,
+	ToolResultEvent,
+	ToolResultEventResult,
 	TurnEndEvent,
 	TurnStartEvent,
 } from "./core/hooks/index.js";