Phase 5: Guardian Mode — continuous awareness + proactive AI alerts

- reactor.py: v5.0.0; guardian_loop() background task scans all agents every
  120s; checks CPU/mem/disk thresholds + agent offline transitions + failed
  services; 10min cooldown per metric to debounce repeat alerts; AI analysis
  of critical findings via Claude; proactive chat injection into conversations
  table; handle_sitrep() generates Iron Man-style full/brief situation reports;
  handle_guardian_config() reads/writes guardian_config table; FastAPI endpoints:
  /guardian/status, /guardian/events, /guardian/events/{id}/ack, /guardian/chat
- arc.php: guardian_status, guardian_events, guardian_ack, guardian_chat actions
- chat.php: Tier 0.9d detects sitrep/situation report/how are things commands
- index.html: GUARDIAN tab in right panel; guardian event list with severity
  badges + AI analysis; ACK / ACK ALL buttons; Guardian badge in bottom bar
  (green/amber/red pulse based on unread critical events); proactive chat
  polling every 30s surfacing guardian-injected messages as JARVIS speech
- admin/index.php: GUARDIAN MODE tab; status bar + events table + config modal;
  inline SITREP runner with result modal; threshold configuration

api/endpoints/arc.php

@@ -179,6 +179,40 @@ switch ($action) {
         echo json_encode(arc_request('DELETE', "/screenshots/{$id}"));
         break;
 
+    // ── GUARDIAN MODE ─────────────────────────────────────────────────────────
+    case 'guardian_status':
+        echo json_encode(arc_request('GET', '/guardian/status'));
+        break;
+
+    case 'guardian_events':
+        $limit    = (int)($_GET['limit'] ?? 30);
+        $unread   = !empty($_GET['unread']) ? 'true' : '';
+        $severity = $_GET['severity'] ?? '';
+        $since    = $_GET['since'] ?? '';
+        $qs = http_build_query(array_filter([
+            'limit'    => $limit,
+            'unread'   => $unread,
+            'severity' => $severity,
+            'since'    => $since,
+        ]));
+        echo json_encode(arc_request('GET', '/guardian/events' . ($qs ? "?{$qs}" : '')));
+        break;
+
+    case 'guardian_ack':
+        $id = (int)($_GET['id'] ?? $data['id'] ?? 0);
+        if ($id) {
+            echo json_encode(arc_request('POST', "/guardian/events/{$id}/ack"));
+        } else {
+            echo json_encode(arc_request('POST', '/guardian/events/ack_all'));
+        }
+        break;
+
+    case 'guardian_chat':
+        $since = $_GET['since'] ?? '';
+        $qs    = $since ? '?since=' . urlencode($since) : '';
+        echo json_encode(arc_request('GET', '/guardian/chat' . $qs));
+        break;
+
     default:
         http_response_code(404);
         echo json_encode(['error' => "Unknown arc action: {$action}"]);