feat: admin Text Gen tool — chapter names + book description via CF Workers AI

Adds backend handlers and SvelteKit UI for an admin text generation tool.
The tool lets admins propose and apply AI-generated chapter titles and book
descriptions using Cloudflare Workers AI (12 LLM models, model selector shared
across both tabs).

ui/src/lib/paraglide/messages/_index.js

@@ -334,6 +334,7 @@ export * from './admin_nav_audio.js'
 export * from './admin_nav_translation.js'
 export * from './admin_nav_changelog.js'
 export * from './admin_nav_image_gen.js'
+export * from './admin_nav_text_gen.js'
 export * from './admin_nav_feedback.js'
 export * from './admin_nav_errors.js'
 export * from './admin_nav_analytics.js'

ui/src/lib/paraglide/messages/admin_nav_text_gen.js

@@ -0,0 +1,44 @@
+/* eslint-disable */
+import { getLocale, experimentalStaticLocale } from '../runtime.js';
+
+/** @typedef {import('../runtime.js').LocalizedString} LocalizedString */
+
+/** @typedef {{}} Admin_Nav_Text_GenInputs */
+
+const en_admin_nav_text_gen = /** @type {(inputs: Admin_Nav_Text_GenInputs) => LocalizedString} */ () => {
+	return /** @type {LocalizedString} */ (`Text Gen`)
+};
+
+const ru_admin_nav_text_gen = /** @type {(inputs: Admin_Nav_Text_GenInputs) => LocalizedString} */ () => {
+	return /** @type {LocalizedString} */ (`Text Gen`)
+};
+
+const id_admin_nav_text_gen = /** @type {(inputs: Admin_Nav_Text_GenInputs) => LocalizedString} */ () => {
+	return /** @type {LocalizedString} */ (`Text Gen`)
+};
+
+const pt_admin_nav_text_gen = /** @type {(inputs: Admin_Nav_Text_GenInputs) => LocalizedString} */ () => {
+	return /** @type {LocalizedString} */ (`Text Gen`)
+};
+
+const fr_admin_nav_text_gen = /** @type {(inputs: Admin_Nav_Text_GenInputs) => LocalizedString} */ () => {
+	return /** @type {LocalizedString} */ (`Text Gen`)
+};
+
+/**
+* | output |
+* | --- |
+* | "Text Gen" |
+*
+* @param {Admin_Nav_Text_GenInputs} inputs
+* @param {{ locale?: "en" | "ru" | "id" | "pt" | "fr" }} options
+* @returns {LocalizedString}
+*/
+export const admin_nav_text_gen = /** @type {((inputs?: Admin_Nav_Text_GenInputs, options?: { locale?: "en" | "ru" | "id" | "pt" | "fr" }) => LocalizedString) & import('../runtime.js').MessageMetadata<Admin_Nav_Text_GenInputs, { locale?: "en" | "ru" | "id" | "pt" | "fr" }, {}>} */ ((inputs = {}, options = {}) => {
+	const locale = experimentalStaticLocale ?? options.locale ?? getLocale()
+	if (locale === "en") return en_admin_nav_text_gen(inputs)
+	if (locale === "ru") return ru_admin_nav_text_gen(inputs)
+	if (locale === "id") return id_admin_nav_text_gen(inputs)
+	if (locale === "pt") return pt_admin_nav_text_gen(inputs)
+	return fr_admin_nav_text_gen(inputs)
+});