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/hero/page.tsx

@@ -0,0 +1,43 @@
+"use client";
+
+import { SectionEditor } from "../_components/SectionEditor";
+import { InputField } from "../_components/FormField";
+
+interface HeroData {
+  headline: string;
+  subheadline: string;
+  ctaText: string;
+  ctaHref: string;
+}
+
+export default function HeroEditorPage() {
+  return (
+    <SectionEditor<HeroData> sectionKey="hero" title="Главный экран">
+      {(data, update) => (
+        <>
+          <InputField
+            label="Заголовок"
+            value={data.headline}
+            onChange={(v) => update({ ...data, headline: v })}
+          />
+          <InputField
+            label="Подзаголовок"
+            value={data.subheadline}
+            onChange={(v) => update({ ...data, subheadline: v })}
+          />
+          <InputField
+            label="Текст кнопки"
+            value={data.ctaText}
+            onChange={(v) => update({ ...data, ctaText: v })}
+          />
+          <InputField
+            label="Ссылка кнопки"
+            value={data.ctaHref}
+            onChange={(v) => update({ ...data, ctaHref: v })}
+            type="url"
+          />
+        </>
+      )}
+    </SectionEditor>
+  );
+}