fix: add Pylon relay fallback to /probe/:id endpoint

The lightweight probe endpoint used by the dashboard for live status
checks had no Pylon integration. When DNS2 (Singapore) tried to probe
home network services directly, all probes timed out with 502. Now
falls back to the configured Pylon relay before the domain fallback.

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

dashcaddy-api/src/app.js

@@ -487,6 +487,28 @@ async function createApp() {
         statusCode = await makeRequest('GET');
       }
     } catch {
+      // Direct probe failed — try Pylon relay if configured
+      const pylonConfig = config.siteConfig?.pylon;
+      if (pylonConfig?.url) {
+        try {
+          const pylonUrl = `${pylonConfig.url}/probe?url=${encodeURIComponent(url)}`;
+          const headers = { 'User-Agent': APP.USER_AGENTS.PROBE };
+          if (pylonConfig.key) headers['x-pylon-key'] = pylonConfig.key;
+          const controller = new AbortController();
+          const pylonTimeout = setTimeout(() => controller.abort(), 8000);
+          const pylonRes = await fetchT(pylonUrl, { method: 'GET', signal: controller.signal, headers });
+          clearTimeout(pylonTimeout);
+          if (pylonRes.ok) {
+            const data = await pylonRes.json();
+            statusCode = data.statusCode || 502;
+          }
+        } catch {
+          // Pylon also failed — fall through to domain fallback
+        }
+      }
+
+      // Domain-based fallback (last resort)
+      if (!statusCode) {
         const fallbackUrl = `https://${config.buildDomain(id)}`;
         const fp = new URL(fallbackUrl);
         statusCode = await new Promise((resolve, reject) => {
@@ -505,7 +527,8 @@ async function createApp() {
           fReq.on('error', reject);
           fReq.on('timeout', () => { fReq.destroy(); reject(new Error('Timeout')); });
           fReq.end();
-      });
+        }).catch(() => 502);
+      }
     }
 
     res.status(statusCode).send();