feat(api): Add preflight columns to worker registry API response

Exposes curl_ip, http_ip, preflight_status, preflight_at, and fingerprint_data
in the /api/worker-registry/workers response.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

backend/src/routes/worker-registry.ts

@@ -355,6 +355,12 @@ router.get('/workers', async (req: Request, res: Response) => {
         -- Decommission fields
         COALESCE(decommission_requested, false) as decommission_requested,
         decommission_reason,
+        -- Preflight fields (dual-transport verification)
+        curl_ip,
+        http_ip,
+        preflight_status,
+        preflight_at,
+        fingerprint_data,
         -- Full metadata for resources
         metadata,
         EXTRACT(EPOCH FROM (NOW() - last_heartbeat_at)) as seconds_since_heartbeat,