Add Zabbix API token authentication support

ZABBIX_API_TOKEN env var can now be used instead of ZABBIX_USER +
ZABBIX_PASSWORD. When set, the token is passed directly as the auth
value in JSON-RPC calls and no login/logout session is created.

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

app/zabbix.py

@@ -10,7 +10,7 @@ Each Yodeck player becomes a Zabbix host with:
 import logging
 import requests
 from app.config import (
-    ZABBIX_URL, ZABBIX_USER, ZABBIX_PASSWORD,
+    ZABBIX_URL, ZABBIX_API_TOKEN, ZABBIX_USER, ZABBIX_PASSWORD,
     ZABBIX_HOST_GROUP, ZABBIX_SNMP_COMMUNITY,
     APP_HOST, ENTERPRISE_OID,
 )
@@ -47,9 +47,14 @@ class ZabbixClient:
         return body['result']
 
     def login(self):
-        self._auth = self._call('user.login', {'user': ZABBIX_USER, 'password': ZABBIX_PASSWORD})
+        if ZABBIX_API_TOKEN:
+            self._auth = ZABBIX_API_TOKEN   # API token used directly — no session needed
+        else:
+            self._auth = self._call('user.login', {'user': ZABBIX_USER, 'password': ZABBIX_PASSWORD})
 
     def logout(self):
+        if ZABBIX_API_TOKEN:
+            return  # API tokens have no session to invalidate
         try:
             self._call('user.logout', [])
         except Exception: