Implement platform settings (Stage 9)

- Wire settings to actual platform behavior: maintenance mode, registration toggle,
  notification emails, curator feedback emails, email verification flag
- Add logo (logoUrl, showLogo) and social network links (YouTube, VK, Telegram) settings
- Show logo + school name dynamically in student layout header
- Add footer to student layout with org requisites and social links
- Register page: read settings server-side, validate terms checkbox with legal links
- Login page: show notice when redirected from closed registration
- Settings form: add Logo and Social Networks sections

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

src/lib/actions/student-actions.ts

@@ -5,6 +5,7 @@ import { auth } from "@/lib/auth";
 import { headers } from "next/headers";
 import { revalidatePath } from "next/cache";
 import { sendHomeworkSubmittedEmail } from "@/lib/email";
+import { getSettings, parseNotificationEmails, asBool } from "@/lib/settings";
 
 // ── Lesson Progress ───────────────────────────────────────────────────────────
 
@@ -72,20 +73,24 @@ export async function submitHomework(
     });
     submissionId = created.id;
 
-    const [lesson, admins] = await Promise.all([
+    const [lesson, settings] = await Promise.all([
       prisma.homework.findUnique({
         where: { id: homeworkId },
         include: { lesson: { select: { title: true } } },
       }),
-      prisma.user.findMany({
-        where: { role: { in: ["admin", "curator"] } },
-        select: { email: true, name: true },
-      }),
+      getSettings(),
     ]);
-    if (lesson) {
+    if (lesson && asBool(settings.notifyOnHomework)) {
+      const configuredEmails = parseNotificationEmails(settings.notificationEmails);
+      const recipients = configuredEmails.length > 0
+        ? configuredEmails.map((email) => ({ email, name: "" }))
+        : await prisma.user.findMany({
+            where: { role: { in: ["admin", "curator"] } },
+            select: { email: true, name: true },
+          });
       await Promise.all(
-        admins.map((a) =>
-          sendHomeworkSubmittedEmail(a.email, a.name, session.user.name, lesson.lesson.title, submissionId)
+        recipients.map((r) =>
+          sendHomeworkSubmittedEmail(r.email, r.name, session.user.name, lesson.lesson.title, submissionId)
         )
       );
     }

src/lib/settings.ts

@@ -33,6 +33,15 @@ export const SETTINGS_DEFAULTS = {
   curatorCanAnswerQuestions: "true",
   curatorCanSeeStudents: "true",
 
+  // Logo
+  logoUrl: "",
+  showLogo: "true",
+
+  // Social networks
+  socialYoutube: "",
+  socialVk: "",
+  socialTelegram: "",
+
   // Code injection
   headCode: "",
   bodyCode: "",