feat (health): voeg helper socket check toe, drie visuele states

Backend (/api/health):
- Importeer HELPER_SOCKET uit common.py
- Voeg helper-check toe: connect() op /run/podman-helper.sock, timeout=2s
- ok blijft true als alleen de helper ontbreekt (waarschuwing, geen fout)
- Nieuwe response key: "helper": {"ok": bool}

Frontend (pingApi / setApiState):
- pingApi() roept nu /api/health aan i.p.v. /pods-dashboard
- setApiState(state, msg) accepteert 'ok' / 'warn' / 'error'
- Gele dot met --warn kleur als helper.ok=false maar core OK
- refreshActive() delegeert statusupdate aan pingApi()
- Detailbericht bij fout: toont welk component (podman/systemd) faalt

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

control/app_system.py

@@ -1,8 +1,10 @@
 import os
+import socket
 import subprocess
 
 from fastapi import APIRouter, HTTPException
 from common import (
+    HELPER_SOCKET,
     _helper_call,
     _podman_get_json as _common_podman_get_json,
     _systemctl as _common_systemctl,
@@ -40,11 +42,21 @@ def init_system_router(session, podman_api_base: str, workloads_dir: str) -> API
         except Exception:
             systemd_reachable = False
 
+        helper_ok = False
+        try:
+            with socket.socket(socket.AF_UNIX, socket.SOCK_STREAM) as s:
+                s.settimeout(2)
+                s.connect(HELPER_SOCKET)
+            helper_ok = True
+        except Exception:
+            helper_ok = False
+
         ok = podman_ok and systemd_reachable
         return {
             "ok": ok,
             "podman": {"ok": podman_ok},
             "systemd_user": {"reachable": systemd_reachable},
+            "helper": {"ok": helper_ok},
         }
 
     @router.get("/test-hybrid")