feat(coding-agent): add experimental first-time setup flow (#5587)

Behind PI_EXPERIMENTAL=1, show a first-time setup dialog on interactive startup when the default agent directory is used and settings.json does not exist. The dialog preselects the detected terminal appearance with an explicit dark/light choice (live preview) and asks for opt-in analytics data sharing. Submitting writes settings.json, which serves as the completion marker; opting in stores a generated trackingId. Escape at any point skips out of setup.

packages/coding-agent/src/modes/interactive/components/index.ts

@@ -13,6 +13,11 @@ export { DynamicBorder } from "./dynamic-border.ts";
 export { ExtensionEditorComponent } from "./extension-editor.ts";
 export { ExtensionInputComponent } from "./extension-input.ts";
 export { ExtensionSelectorComponent } from "./extension-selector.ts";
+export {
+	FirstTimeSetupComponent,
+	type FirstTimeSetupOptions,
+	type FirstTimeSetupResult,
+} from "./first-time-setup.ts";
 export { FooterComponent } from "./footer.ts";
 export { keyHint, keyText, rawKeyHint } from "./keybinding-hints.ts";
 export { LoginDialogComponent } from "./login-dialog.ts";