Multi-User-Plattform: jeder Benutzer hat eigene, isolierte Daten

- Auth via Session-Cookie + Login-Seite (scrypt, lib/password.js, sessions-Tabelle)
- AsyncLocalStorage (lib/context.js) propagiert aktuellen Benutzer durch alle Libs
- user_id auf allen Datentabellen (FK->users ON DELETE CASCADE), per-user PK/UNIQUE
  (app_state, settings, prompts, design, jobangebote) und per-user Dateispeicher
  (data/<dir>/<userId>/)
- Alle Queries in server.js + lib/api.js nach user_id scope-iert
- Pro-Benutzer-Konfiguration (Ollama/Mail/CalDAV/API-Token) in app_state,
  Live gelesen via config.get(); Hintergrund-Loops (IMAP/CalDAV) iterieren alle Benutzer
- REST-API /api/v1: X-API-Key loest den Token zu einem Benutzer auf, Anfragen
  operieren nur auf dessen Daten
- Admin-Panel /admin: Benutzer anlegen, Passwort zuruecksetzen, loeschen (mit Daten)
- Idempotente Migration (lib/migrate-multiuser.js + scripts/migrate-to-multiuser.js):
  bestehende Daten werden dem Benutzer admin:admin zugeordnet

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

lib/password.js

@@ -0,0 +1,34 @@
+// Password hashing using Node's built-in scrypt + a per-hash random salt.
+//
+// No external dependency (bcrypt would need a native build step). scrypt is
+// memory-hard and well suited for interactive logins. Hash format:
+//   "<saltHex>:<hashHex>"  (salt is 16 bytes, hash is 64 bytes)
+
+const crypto = require('crypto');
+
+const KEYLEN = 64;
+
+function hash(password) {
+  const salt = crypto.randomBytes(16).toString('hex');
+  const out = crypto.scryptSync(password, salt, KEYLEN).toString('hex');
+  return `${salt}:${out}`;
+}
+
+function verify(password, stored) {
+  if (typeof stored !== 'string' || !stored.includes(':')) return false;
+  const idx = stored.indexOf(':');
+  const salt = stored.slice(0, idx);
+  const expected = stored.slice(idx + 1);
+  if (!salt || !expected) return false;
+  let computed;
+  try {
+    computed = crypto.scryptSync(password, salt, KEYLEN).toString('hex');
+  } catch (e) {
+    return false;
+  }
+  if (computed.length !== expected.length) return false;
+  // Constant-time compare to avoid timing side channels.
+  return crypto.timingSafeEqual(Buffer.from(computed), Buffer.from(expected));
+}
+
+module.exports = { hash, verify };