Replace Vazirmatn with a locally-served Peyda font for Persian text.

Vendor the Peyda woff weights (Thin–Black) under public/fonts/peyda and
load them via next/font/local in a shared fonts module, exposed through
the --font-peyda CSS variable and the font-peyda Tailwind utility. Drops
the runtime Google Fonts fetch on the landing and auth pages.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

frontend/tailwind.config.ts

@@ -9,7 +9,7 @@ const config: Config = {
   theme: {
     extend: {
       fontFamily: {
-        vazir: ['var(--font-vazir)', 'system-ui', 'sans-serif'],
+        peyda: ['var(--font-peyda)', 'system-ui', 'sans-serif'],
       },
       colors: {
         primary: {