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/admin/_components/SectionEditor.tsx

@@ -0,0 +1,94 @@
+"use client";
+
+import { useState, useEffect, useCallback } from "react";
+import { Save, Loader2, Check } from "lucide-react";
+
+interface SectionEditorProps<T> {
+  sectionKey: string;
+  title: string;
+  children: (data: T, update: (data: T) => void) => React.ReactNode;
+}
+
+export function SectionEditor<T>({
+  sectionKey,
+  title,
+  children,
+}: SectionEditorProps<T>) {
+  const [data, setData] = useState<T | null>(null);
+  const [loading, setLoading] = useState(true);
+  const [saving, setSaving] = useState(false);
+  const [saved, setSaved] = useState(false);
+  const [error, setError] = useState("");
+
+  useEffect(() => {
+    fetch(`/api/admin/sections/${sectionKey}`)
+      .then((r) => {
+        if (!r.ok) throw new Error("Failed to load");
+        return r.json();
+      })
+      .then(setData)
+      .catch(() => setError("Не удалось загрузить данные"))
+      .finally(() => setLoading(false));
+  }, [sectionKey]);
+
+  const handleSave = useCallback(async () => {
+    if (!data) return;
+    setSaving(true);
+    setSaved(false);
+    setError("");
+
+    try {
+      const res = await fetch(`/api/admin/sections/${sectionKey}`, {
+        method: "PUT",
+        headers: { "Content-Type": "application/json" },
+        body: JSON.stringify(data),
+      });
+      if (!res.ok) throw new Error("Failed to save");
+      setSaved(true);
+      setTimeout(() => setSaved(false), 2000);
+    } catch {
+      setError("Ошибка сохранения");
+    } finally {
+      setSaving(false);
+    }
+  }, [data, sectionKey]);
+
+  if (loading) {
+    return (
+      <div className="flex items-center gap-2 text-neutral-400">
+        <Loader2 size={18} className="animate-spin" />
+        Загрузка...
+      </div>
+    );
+  }
+
+  if (!data) {
+    return <p className="text-red-400">{error || "Данные не найдены"}</p>;
+  }
+
+  return (
+    <div>
+      <div className="flex items-center justify-between gap-4">
+        <h1 className="text-2xl font-bold">{title}</h1>
+        <button
+          onClick={handleSave}
+          disabled={saving}
+          className="flex items-center gap-2 rounded-lg bg-gold px-4 py-2.5 text-sm font-medium text-black transition-opacity hover:opacity-90 disabled:opacity-50"
+        >
+          {saving ? (
+            <Loader2 size={16} className="animate-spin" />
+          ) : saved ? (
+            <Check size={16} />
+          ) : (
+            <Save size={16} />
+          )}
+          {saving ? "Сохранение..." : saved ? "Сохранено!" : "Сохранить"}
+        </button>
+      </div>
+
+      {error && <p className="mt-4 text-sm text-red-400">{error}</p>}
+
+      <div className="mt-6 space-y-6">{children(data, setData)}</div>
+    </div>
+  );
+}