feat: add master classes section with registration system

- New master classes section on landing page with upcoming events grid
- Admin CRUD for master classes (image, slots, trainer, style, cost, location)
- User signup modal (name + Instagram required, Telegram optional)
- Admin registration management: view, add, edit, delete with quick-contact links
- Customizable success message for signup confirmation
- Auto-filter past events, Russian date formatting, duration auto-calculation

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/app/page.tsx

@@ -2,6 +2,7 @@ import { Hero } from "@/components/sections/Hero";
 import { Team } from "@/components/sections/Team";
 import { About } from "@/components/sections/About";
 import { Classes } from "@/components/sections/Classes";
+import { MasterClasses } from "@/components/sections/MasterClasses";
 import { Schedule } from "@/components/sections/Schedule";
 import { Pricing } from "@/components/sections/Pricing";
 import { FAQ } from "@/components/sections/FAQ";
@@ -29,6 +30,7 @@ export default function HomePage() {
         />
         <Team data={content.team} schedule={content.schedule.locations} />
         <Classes data={content.classes} />
+        <MasterClasses data={content.masterClasses} />
         <Schedule data={content.schedule} classItems={content.classes.items} />
         <Pricing data={content.pricing} />
         <FAQ data={content.faq} />