Build fixes: offline-safe fonts, Next.js API route type updates, TS strict errors resolved, MUI import cleanup, chat markdown wrapper, Azure OpenAI typing, caching key + chapter API id types, and misc error-logging typings.

lib/fonts.ts

@@ -1,15 +1,25 @@
-import { Merriweather, Lato } from 'next/font/google'
+// Offline-safe font shim for builds without network access.
+// Provides the minimal shape used by the app: `.style.fontFamily` and `.variable`.
 
-export const merriweather = Merriweather({
-  subsets: ['latin'],
-  weight: ['300', '400', '700', '900'],
-  variable: '--font-merriweather',
-  display: 'swap',
-})
+type FontShim = {
+  style: { fontFamily: string }
+  variable: string
+}
 
-export const lato = Lato({
-  subsets: ['latin'],
-  weight: ['300', '400', '700', '900'],
-  variable: '--font-lato',
-  display: 'swap',
-})
+export const merriweather: FontShim = {
+  // Prefer Merriweather if available on the system, otherwise common serif fallbacks
+  style: {
+    fontFamily: 'Merriweather, Georgia, "Times New Roman", Times, serif',
+  },
+  // Not using next/font CSS variable when offline
+  variable: '',
+}
+
+export const lato: FontShim = {
+  // Prefer Lato if available on the system, otherwise robust system sans fallbacks
+  style: {
+    fontFamily:
+      'Lato, -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, "Helvetica Neue", Arial, "Noto Sans", sans-serif, "Apple Color Emoji", "Segoe UI Emoji", "Segoe UI Symbol"',
+  },
+  variable: '',
+}