Fix mixed content: ProxyFix for HTTPS behind nginx, set PREFERRED_URL_SCHEME=https

app.py

@@ -423,6 +423,11 @@ AGENT_KEYWORDS = {
 app.secret_key = os.getenv('SECRET_KEY', 'agent-orchestration-secret-key-2026')
 app.config['UPLOAD_FOLDER'] = 'uploads'
 app.config['MAX_CONTENT_LENGTH'] = 16 * 1024 * 1024
+app.config['PREFERRED_URL_SCHEME'] = 'https'
+
+# Hinter nginx: X-Forwarded-Proto auswerten damit Flask HTTPS-URLs generiert
+from werkzeug.middleware.proxy_fix import ProxyFix
+app.wsgi_app = ProxyFix(app.wsgi_app, x_proto=1, x_host=1)
 app.permanent_session_lifetime = timedelta(days=7)
 
 # ── App Password ─────────────────────────────────────────────────────────────