Voeg tenant beheer toe aan rikx-offerte

- Login pagina met HMAC-sessie authenticatie
- /tenants overzicht: lijst alle rikx-platform accounts
- Nieuw tenant aanmaken (naam, slug, admin gebruiker)
- Tenant verwijderen (cascade via foreign keys)
- Leest rikx-platform SQLite DB via /rikx-platform-data mount
- Homepage redirect naar /tenants of /login

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

lib/platform-db.ts

@@ -0,0 +1,42 @@
+import { DatabaseSync } from "node:sqlite";
+
+const DB_PATH = process.env.RIKX_PLATFORM_DB_PATH || "/rikx-platform-data/app.db";
+
+let _db: DatabaseSync | null = null;
+
+export function getPlatformDb(): DatabaseSync {
+  if (!_db) {
+    _db = new DatabaseSync(DB_PATH);
+    _db.exec("PRAGMA journal_mode = WAL");
+    _db.exec("PRAGMA foreign_keys = ON");
+  }
+  return _db;
+}
+
+export type PlatformAccount = {
+  id: number;
+  name: string;
+  slug: string;
+  created_at: string;
+};
+
+export type PlatformUser = {
+  id: number;
+  account_id: number;
+  email: string;
+  name: string;
+  role: string;
+  created_at: string;
+};
+
+export function listAccounts(): (PlatformAccount & { user_count: number })[] {
+  return getPlatformDb()
+    .prepare(
+      `SELECT a.*, COUNT(u.id) as user_count
+       FROM accounts a
+       LEFT JOIN users u ON u.account_id = a.id
+       GROUP BY a.id
+       ORDER BY a.created_at DESC`
+    )
+    .all() as (PlatformAccount & { user_count: number })[];
+}