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/lib/content.ts

@@ -0,0 +1,13 @@
+import { getSiteContent } from "@/lib/db";
+import { siteContent as fallback } from "@/data/content";
+import type { SiteContent } from "@/types/content";
+
+export function getContent(): SiteContent {
+  try {
+    const content = getSiteContent();
+    if (content) return content;
+    return fallback;
+  } catch {
+    return fallback;
+  }
+}