Add ui.custom() for custom hook components with keyboard focus

- Add custom() to HookUIContext: returns { close, requestRender }
- Component receives keyboard input via handleInput()
- CustomMessageComponent default rendering now limits to 5 lines when collapsed
- Add snake.ts example hook with /snake command

packages/coding-agent/src/core/hooks/index.ts

@@ -13,8 +13,6 @@ export type {
 	AgentEndEvent,
 	AgentStartEvent,
 	BashToolResultEvent,
-	HookMessageRenderer,
-	HookMessageRenderOptions,
 	CustomToolResultEvent,
 	EditToolResultEvent,
 	ExecOptions,
@@ -28,6 +26,8 @@ export type {
 	HookEventContext,
 	HookFactory,
 	HookMessage,
+	HookMessageRenderer,
+	HookMessageRenderOptions,
 	HookUIContext,
 	LsToolResultEvent,
 	ReadToolResultEvent,