refactor(api): use knex for database operations

backend/db/init.js

@@ -0,0 +1,53 @@
+import knex from 'knex';
+import { fileURLToPath } from 'url';
+import { dirname } from 'path';
+import config from '../knexfile.js';
+
+const __filename = fileURLToPath(import.meta.url);
+const __dirname = dirname(__filename);
+
+let db = null;
+
+export async function getDB() {
+  if (!db) {
+    db = knex(config);
+    await db.migrate.latest();
+  }
+  return db;
+}
+
+export async function initDB() {
+  const db = await getDB();
+  
+  const existing = await db('cv_data').where({ id: 1 }).first();
+  if (!existing) {
+    await db('cv_data').insert({
+      id: 1,
+      data: JSON.stringify({
+        personal: {
+          name: "Tuan-Dat Tran",
+          title: "Junior DevOps Engineer",
+          intro: "Passionierter DevOps Engineer mit Fokus auf Cloud-Infrastruktur.",
+          email: "tuan-dat.tran@example.com",
+          github: "https://github.com/tuan-dat-tran",
+          linkedin: "https://linkedin.com/in/tuan-dat-tran",
+          location: "Deutschland"
+        },
+        experience: [],
+        skills: {},
+        education: [],
+        projects: []
+      })
+    });
+    console.log('Initialized database with default CV data');
+  }
+  
+  console.log('Database initialized');
+}
+
+export async function closeDB() {
+  if (db) {
+    await db.destroy();
+    db = null;
+  }
+}