feat: Schritte 14–15 — Google Calendar OAuth + Apple CalDAV Sync + Settings-Seite

- server/services/google-calendar.js: OAuth 2.0, bidirektionaler Sync via
  Google Calendar API v3, inkrementeller syncToken, 410-Fallback auf Vollsync
- server/services/apple-calendar.js: CalDAV via tsdav (dynamic ESM import),
  minimaler ICS-Parser + ICS-Builder, bidirektionaler Sync
- server/routes/calendar.js: 7 neue Sync-Routen (google/auth, google/callback,
  google/sync, google/status, google/disconnect, apple/status, apple/sync)
- server/db.js: Migration 2 — sync_config Tabelle + idx_calendar_external_id
- server/db-schema-test.js: MIGRATIONS_SQL[2] für Tests synchronisiert
- server/auth.js: PATCH /me/password Endpoint
- server/index.js: Auto-Sync-Scheduler (setInterval, SYNC_INTERVAL_MINUTES)
- public/pages/settings.js: vollständige Settings-Seite (Konto, Passwort,
  Kalender-Sync-Status + Aktionen, Familienmitglieder-Verwaltung)
- public/styles/settings.css: neue Stylesheet-Datei
- public/index.html + public/sw.js: settings.css eingebunden und gecacht
- .env.example: SYNC_INTERVAL_MINUTES ergänzt
- README.md: vollständige Setup-Anleitung, Google/Apple-Sync-Dokumentation,
  modernes GitHub-Layout mit Badges und aufklappbaren Abschnitten

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

server/index.js

@@ -11,9 +11,11 @@ const express    = require('express');
 const helmet     = require('helmet');
 const rateLimit  = require('express-rate-limit');
 const path       = require('path');
-const db         = require('./db');
+const db             = require('./db');
 const { router: authRouter, sessionMiddleware, requireAuth } = require('./auth');
 const { csrfMiddleware } = require('./middleware/csrf');
+const googleCalendar = require('./services/google-calendar');
+const appleCalendar  = require('./services/apple-calendar');
 
 const app = express();
 const PORT = process.env.PORT || 3000;
@@ -154,12 +156,37 @@ app.use((err, req, res, _next) => {
   res.status(500).json({ error: 'Interner Serverfehler.', code: 500 });
 });
 
+// --------------------------------------------------------
+// Auto-Sync Scheduler (Google + Apple Calendar)
+// --------------------------------------------------------
+
+const SYNC_INTERVAL_MS = (parseInt(process.env.SYNC_INTERVAL_MINUTES, 10) || 15) * 60_000;
+
+async function runSync() {
+  const { connected: googleConnected } = googleCalendar.getStatus();
+  if (googleConnected) {
+    googleCalendar.sync().catch((e) => console.error('[Sync] Google Fehler:', e.message));
+  }
+
+  const { configured: appleConfigured } = appleCalendar.getStatus();
+  if (appleConfigured) {
+    appleCalendar.sync().catch((e) => console.error('[Sync] Apple Fehler:', e.message));
+  }
+}
+
 // --------------------------------------------------------
 // Server starten
 // --------------------------------------------------------
 app.listen(PORT, () => {
   console.log(`[Oikos] Server läuft auf Port ${PORT}`);
   console.log(`[Oikos] Umgebung: ${process.env.NODE_ENV || 'development'}`);
+
+  // Erster Sync nach 10 Sekunden (warten bis DB vollständig initialisiert)
+  setTimeout(() => {
+    runSync();
+    setInterval(runSync, SYNC_INTERVAL_MS);
+    console.log(`[Sync] Auto-Sync alle ${SYNC_INTERVAL_MS / 60_000} Minuten aktiv.`);
+  }, 10_000);
 });
 
 module.exports = app;