feat: admin panel with SQLite, auth, and calendar-style schedule editor

Complete admin panel for content management:
- SQLite database with better-sqlite3, seed script from content.ts
- Simple password auth with HMAC-signed cookies (Edge + Node compatible)
- 9 section editors: meta, hero, about, team, classes, schedule, pricing, FAQ, contact
- Team CRUD with image upload and drag reorder
- Schedule editor with Google Calendar-style visual timeline (colored blocks, overlap detection, click-to-add)
- All public components refactored to accept data props from DB (with fallback to static content)
- Middleware protecting /admin/* and /api/admin/* routes

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

src/app/api/auth/login/route.ts

@@ -0,0 +1,23 @@
+import { NextRequest, NextResponse } from "next/server";
+import { verifyPassword, signToken, COOKIE_NAME } from "@/lib/auth";
+
+export async function POST(request: NextRequest) {
+  const body = await request.json() as { password?: string };
+
+  if (!body.password || !verifyPassword(body.password)) {
+    return NextResponse.json({ error: "Неверный пароль" }, { status: 401 });
+  }
+
+  const token = signToken();
+  const response = NextResponse.json({ ok: true });
+
+  response.cookies.set(COOKIE_NAME, token, {
+    httpOnly: true,
+    secure: process.env.NODE_ENV === "production",
+    sameSite: "lax",
+    path: "/",
+    maxAge: 60 * 60 * 24, // 24 hours
+  });
+
+  return response;
+}