Differentiate API key missing vs API unreachable in monitor banner

unraid_api.php: track key_missing separately from general fallbacks.
  vv_api_data() sets key_missing=true when HOST*_UNRAID_API_KEY is empty.
  vv_api_get_status() includes key_missing in the status payload.

monitor.php: two distinct banner states instead of one orange warning.
  key_missing → subtle dark/grey note: "API key not configured — add
    HOST1_UNRAID_API_KEY in Scheduler → host conf to enable enhanced monitoring"
  key present but unreachable → existing orange ⚠ with fallback list.
  No banner at all when API is working correctly.

Plugin/unraid/include/unraid_api.php

@@ -17,17 +17,19 @@ require_once __DIR__ . '/config.php';
 // ── Fallback tracking ─────────────────────────────────────────────────────────
 
 function &_vv_api_fallbacks(): array { static $f = []; return $f; }
+function &_vv_api_key_missing(): bool { static $m = false; return $m; }
 
 function vv_api_record_fallback(string $fn): void {
-    $f  = &_vv_api_fallbacks();
+    $f   = &_vv_api_fallbacks();
     $f[] = $fn;
 }
 
 function vv_api_get_status(): array {
     $fallbacks = array_unique(_vv_api_fallbacks());
     return [
-        'available' => empty($fallbacks),
-        'fallbacks' => $fallbacks,
+        'available'   => empty($fallbacks),
+        'key_missing' => _vv_api_key_missing(),
+        'fallbacks'   => $fallbacks,
     ];
 }
 
@@ -43,7 +45,12 @@ function vv_api_data(): ?array {
     $hostId = vv_detect_host();
     $vars   = vv_conf_vars();
     $key    = $vars[strtoupper($hostId) . '_UNRAID_API_KEY'] ?? '';
-    if (!$key) { $cache = null; return null; }
+    if (!$key) {
+        $m = &_vv_api_key_missing();
+        $m = true;
+        $cache = null;
+        return null;
+    }
 
     // Fields verified against live schema introspection (2026-05-29).
     // array.parities / .disks / .caches are SEPARATE lists — .disks is DATA only.