fix(httpclient): replace DefaultClient with timed clients and retry

Пакет httpclient: timeout 45s, idle pool, DoWithRetry. Scheduler и nodecli
используют retry; pipeline/asnresolve/jobs — httpclient.New вместо DefaultClient.

Co-authored-by: Cursor <cursoragent@cursor.com>

internal/httpapi/bootstrap.go

@@ -7,6 +7,7 @@ import (
 	"time"
 
 	"evobgp/internal/db"
+	"evobgp/internal/httpclient"
 	"evobgp/internal/jobs"
 	"evobgp/internal/observability"
 	"evobgp/internal/repository"
@@ -17,7 +18,7 @@ import (
 
 // NewCDNHTTPClient returns the shared HTTP client for CDN and preview fetches (PERF-02 / ERR-03).
 func NewCDNHTTPClient() *http.Client {
-	return &http.Client{Timeout: 45 * time.Second}
+	return httpclient.New(httpclient.DefaultTimeout)
 }
 
 // BootstrapWorkers opens the same store.Backend and jobs.Registry as New (without HTTP or bundle keys).