feat(coding-agent): add ctx.ui.setEditorComponent() extension API

- Add setEditorComponent() to ctx.ui for custom editor components
- Add CustomEditor base class for extensions (handles app keybindings)
- Add keybindings parameter to ctx.ui.custom() factory (breaking change)
- Add modal-editor.ts example (vim-like modes)
- Add rainbow-editor.ts example (animated text highlighting)
- Update docs: extensions.md, tui.md Pattern 7
- Clean up terminal on TUI render errors

packages/coding-agent/src/index.ts

@@ -40,6 +40,7 @@ export type {
 	AgentStartEvent,
 	AgentToolResult,
 	AgentToolUpdateCallback,
+	AppAction,
 	BeforeAgentStartEvent,
 	ContextEvent,
 	ExecOptions,
@@ -55,6 +56,7 @@ export type {
 	ExtensionShortcut,
 	ExtensionUIContext,
 	ExtensionUIDialogOptions,
+	KeybindingsManager,
 	LoadExtensionsResult,
 	LoadedExtension,
 	MessageRenderer,