feat(admin): integrate Next.js admin panel (admin-next/) from feat/nextjs-admin

- Add admin-next/: full Next.js + Prisma + shadcn admin panel (45 API routes, 76 components)
- docker-compose: tg_shop_admin service (port 3000, shared db/shop.db, prisma), bot talks to it via ADMIN_CHAT_URL=http://tg_shop_admin:3000/api/chat
- tor-proxy now proxies onion admin to tg_shop_admin:3000 (new panel)
- chatbotService: ADMIN_CHAT_URL default = http://tg_shop_admin:3000/api/chat (removed localhost:3100 anachronism)
- .env admin secrets gitignored (admin-next/.env)

admin-next/Caddyfile

@@ -0,0 +1,23 @@
+:81 {
+	@transform_port_query {
+		query XTransformPort=*
+	}
+
+	handle @transform_port_query {
+		reverse_proxy localhost:{query.XTransformPort} {
+			header_up Host {host}
+			header_up X-Forwarded-For {remote_host}
+			header_up X-Forwarded-Proto {scheme}
+			header_up X-Real-IP {remote_host}
+		}
+	}
+
+	handle {
+		reverse_proxy localhost:3000 {
+			header_up Host {host}
+			header_up X-Forwarded-For {remote_host}
+			header_up X-Forwarded-Proto {scheme}
+			header_up X-Real-IP {remote_host}
+		}
+	}
+}