feat(cardav): create cardav router with GET /accounts

Add CardDAV API router with GET /accounts endpoint. Returns all
CardDAV accounts from database via cardav-sync service. Added test
infrastructure with _setTestDatabase helper for isolated API testing.

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

server/db.js

@@ -1354,6 +1354,14 @@ function transaction(fn) {
   return get().transaction(fn)();
 }
 
+/**
+ * ONLY FOR TESTING: Override the internal db instance
+ * @param {import('better-sqlite3').Database} testDb
+ */
+function _setTestDatabase(testDb) {
+  db = testDb;
+}
+
 init();   // auto-initialise when module is first imported
 
-export { init, get, transaction, currentVersion, getPath, backupToFile, restoreFromFile, MIGRATIONS };
+export { init, get, transaction, currentVersion, getPath, backupToFile, restoreFromFile, MIGRATIONS, _setTestDatabase };

server/routes/cardav.js

@@ -0,0 +1,33 @@
+/**
+ * Modul: CardDAV Management
+ * Zweck: REST-API-Routen für CardDAV Account Management, Addressbook Discovery, Sync
+ * Abhängigkeiten: express, server/db.js, server/services/cardav-sync.js
+ */
+
+import { createLogger } from '../logger.js';
+import express from 'express';
+import * as db from '../db.js';
+import * as CardDAVSync from '../services/cardav-sync.js';
+import { str, collectErrors, MAX_TITLE } from '../middleware/validate.js';
+
+const log = createLogger('CardDAV');
+const MAX_URL = 500;
+
+const router = express.Router();
+
+/**
+ * GET /api/v1/contacts/cardav/accounts
+ * Liste aller CardDAV Accounts.
+ * Response: { data: Account[] }
+ */
+router.get('/accounts', async (req, res) => {
+  try {
+    const accounts = await CardDAVSync.getAllAccounts();
+    res.json({ data: accounts });
+  } catch (err) {
+    log.error('Error fetching accounts:', err);
+    res.status(500).json({ error: err.message || 'Interner Fehler', code: 500 });
+  }
+});
+
+export default router;

test-carddav.js

@@ -1467,3 +1467,75 @@ describe('Multi-Value Validators', () => {
     });
   });
 });
+
+// ========================================
+// CardDAV API Routes
+// ========================================
+
+describe('CardDAV API Routes', () => {
+  let apiTestDb;
+
+  before(async () => {
+    // Create in-memory test database for API routes
+    apiTestDb = new Database(':memory:');
+    apiTestDb.pragma('foreign_keys = ON');
+
+    // Create minimal schema
+    apiTestDb.exec(`
+      CREATE TABLE users (
+        id INTEGER PRIMARY KEY AUTOINCREMENT,
+        username TEXT NOT NULL
+      );
+
+      CREATE TABLE contacts (
+        id         INTEGER PRIMARY KEY AUTOINCREMENT,
+        name       TEXT NOT NULL,
+        category   TEXT NOT NULL DEFAULT 'Sonstiges',
+        phone      TEXT,
+        email      TEXT,
+        address    TEXT,
+        notes      TEXT,
+        family_user_id INTEGER REFERENCES users(id) ON DELETE CASCADE,
+        created_at TEXT NOT NULL DEFAULT (strftime('%Y-%m-%dT%H:%M:%SZ', 'now')),
+        updated_at TEXT NOT NULL DEFAULT (strftime('%Y-%m-%dT%H:%M:%SZ', 'now'))
+      );
+
+      INSERT INTO users (username) VALUES ('testuser');
+    `);
+
+    // Apply Migration 30 to create CardDAV tables
+    const migration30 = MIGRATIONS.find(m => m.version === 30);
+    if (!migration30) {
+      throw new Error('Migration 30 not found');
+    }
+    apiTestDb.exec(migration30.up);
+
+    // Override db.get() to use our test database
+    const dbModule = await import('./server/db.js');
+    dbModule._setTestDatabase(apiTestDb);
+  });
+
+  describe('Account Management', () => {
+    it('GET /accounts - should return empty array when no accounts', async () => {
+      const cardavRouter = await import('./server/routes/cardav.js');
+
+      const req = { params: {}, query: {}, body: {} };
+      const res = {
+        statusCode: 200,
+        status(code) { this.statusCode = code; return this; },
+        json(data) { this.data = data; return this; },
+      };
+
+      const getHandler = cardavRouter.default.stack.find(
+        layer => layer.route?.path === '/accounts' && layer.route.methods.get
+      )?.route?.stack[0]?.handle;
+
+      assert.ok(getHandler, 'GET /accounts handler should exist');
+      await getHandler(req, res);
+
+      assert.strictEqual(res.statusCode, 200);
+      assert.ok(Array.isArray(res.data.data));
+      assert.strictEqual(res.data.data.length, 0);
+    });
+  });
+});