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/admin/upload/route.ts

@@ -0,0 +1,50 @@
+import { NextRequest, NextResponse } from "next/server";
+import { writeFile, mkdir } from "fs/promises";
+import path from "path";
+
+const ALLOWED_TYPES = ["image/jpeg", "image/png", "image/webp", "image/avif"];
+const MAX_SIZE = 5 * 1024 * 1024; // 5MB
+
+export async function POST(request: NextRequest) {
+  const formData = await request.formData();
+  const file = formData.get("file") as File | null;
+  const folder = (formData.get("folder") as string) || "team";
+
+  if (!file) {
+    return NextResponse.json({ error: "No file provided" }, { status: 400 });
+  }
+
+  if (!ALLOWED_TYPES.includes(file.type)) {
+    return NextResponse.json(
+      { error: "Only JPEG, PNG, WebP, and AVIF are allowed" },
+      { status: 400 }
+    );
+  }
+
+  if (file.size > MAX_SIZE) {
+    return NextResponse.json(
+      { error: "File too large (max 5MB)" },
+      { status: 400 }
+    );
+  }
+
+  // Sanitize filename
+  const ext = path.extname(file.name) || ".webp";
+  const baseName = file.name
+    .replace(ext, "")
+    .toLowerCase()
+    .replace(/[^a-z0-9а-яё-]/gi, "-")
+    .replace(/-+/g, "-")
+    .slice(0, 50);
+  const fileName = `${baseName}-${Date.now()}${ext}`;
+
+  const dir = path.join(process.cwd(), "public", "images", folder);
+  await mkdir(dir, { recursive: true });
+
+  const buffer = Buffer.from(await file.arrayBuffer());
+  const filePath = path.join(dir, fileName);
+  await writeFile(filePath, buffer);
+
+  const publicPath = `/images/${folder}/${fileName}`;
+  return NextResponse.json({ path: publicPath });
+}