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/logout/route.ts

@@ -0,0 +1,12 @@
+import { NextResponse } from "next/server";
+import { COOKIE_NAME } from "@/lib/auth";
+
+export async function POST() {
+  const response = NextResponse.json({ ok: true });
+  response.cookies.set(COOKIE_NAME, "", {
+    httpOnly: true,
+    path: "/",
+    maxAge: 0,
+  });
+  return response;
+}