Add setEditorText/getEditorText to hook UI context, improve custom() API

- Add setEditorText() and getEditorText() to HookUIContext for prompt generator pattern
- custom() now accepts async factories for fire-and-forget work
- Add CancellableLoader component to tui package
- Add BorderedLoader component for hooks with cancel UI
- Export HookAPI, HookContext, HookFactory from main package
- Update all examples to import from packages instead of relative paths
- Update hooks.md and custom-tools.md documentation

fixes #350

packages/coding-agent/examples/sdk/12-full-control.ts

@@ -9,7 +9,6 @@
  */
 
 import { getModel } from "@mariozechner/pi-ai";
-import { Type } from "@sinclair/typebox";
 import {
 	AuthStorage,
 	type CustomTool,
@@ -20,7 +19,8 @@ import {
 	ModelRegistry,
 	SessionManager,
 	SettingsManager,
-} from "../../src/index.js";
+} from "@mariozechner/pi-coding-agent";
+import { Type } from "@sinclair/typebox";
 
 // Custom auth storage location
 const authStorage = new AuthStorage("/tmp/my-agent/auth.json");