fix(iam): preserve CreatedAt across boots + paginate ListProviders

Two medium-priority issues gemini flagged on the read-only IAM API:

1. The static-config bootstrap was setting CreatedAt = time.Now() on
   every server start, so the IAM GetOpenIDConnectProvider response's
   CreateDate shifted on each restart even when backed by a persistent
   store. Look up the existing record via GetProviderByARN first and
   preserve its CreatedAt; only the UpdatedAt advances.

2. FilerOIDCProviderStore.ListProviders had a hardcoded Limit: 1000
   that silently truncated above that. Stream-paginate via
   StartFromFileName, returning io.EOF naturally and surfacing all
   other errors instead of swallowing them.

Addresses two gemini medium reviews on PR #9319.

weed/iam/integration/iam_manager.go

@@ -286,16 +286,24 @@ func (m *IAMManager) initOIDCProviderStore(config *IAMConfig) error {
 			continue
 		}
 		clientIDs := extractClientIDs(pc.Config)
-		now := time.Now()
+		ctx := context.Background()
+		// Preserve CreatedAt across reboots when a persistent store already
+		// has this provider — IAM's GetOpenIDConnectProvider response
+		// shouldn't shift its CreateDate every time the server restarts.
+		now := time.Now().UTC()
+		createdAt := now
+		if existing, err := store.GetProviderByARN(ctx, m.getFilerAddress(), arn); err == nil && existing != nil && !existing.CreatedAt.IsZero() {
+			createdAt = existing.CreatedAt
+		}
 		rec := &OIDCProviderRecord{
 			AccountID: accountID,
 			ARN:       arn,
 			URL:       issuer,
 			ClientIDs: clientIDs,
-			CreatedAt: now,
+			CreatedAt: createdAt,
 			UpdatedAt: now,
 		}
-		if err := store.StoreProvider(context.Background(), m.getFilerAddress(), rec); err != nil {
+		if err := store.StoreProvider(ctx, m.getFilerAddress(), rec); err != nil {
 			glog.Warningf("mirror static OIDC provider %s into store: %v", pc.Name, err)
 		}
 	}

weed/iam/integration/oidc_provider_store.go

@@ -5,7 +5,9 @@ import (
 	"crypto/sha1"
 	"encoding/hex"
 	"encoding/json"
+	"errors"
 	"fmt"
+	"io"
 	"net/url"
 	"sort"
 	"strings"
@@ -281,30 +283,49 @@ func (f *FilerOIDCProviderStore) ListProviders(ctx context.Context, filerAddress
 
 	var out []*OIDCProviderRecord
 	err := f.withFilerClient(filerAddress, func(client filer_pb.SeaweedFilerClient) error {
-		stream, err := client.ListEntries(ctx, &filer_pb.ListEntriesRequest{
-			Directory: f.basePath,
-			Limit:     1000,
-		})
-		if err != nil {
-			return fmt.Errorf("list OIDC providers: %v", err)
-		}
+		// Stream-paginate via StartFromFileName so deployments with more
+		// than 1000 providers don't get a silently truncated list.
+		const pageSize = 1000
+		startFrom := ""
 		for {
-			resp, err := stream.Recv()
+			stream, err := client.ListEntries(ctx, &filer_pb.ListEntriesRequest{
+				Directory:          f.basePath,
+				Limit:              pageSize,
+				StartFromFileName:  startFrom,
+				InclusiveStartFrom: false,
+			})
 			if err != nil {
+				return fmt.Errorf("list OIDC providers: %v", err)
+			}
+			lastName := ""
+			pageCount := 0
+			for {
+				resp, recvErr := stream.Recv()
+				if recvErr != nil {
+					if errors.Is(recvErr, io.EOF) {
+						break
+					}
+					return fmt.Errorf("recv OIDC provider entry: %w", recvErr)
+				}
+				if resp.Entry == nil || resp.Entry.IsDirectory {
+					continue
+				}
+				lastName = resp.Entry.Name
+				pageCount++
+				if !strings.HasSuffix(resp.Entry.Name, ".json") {
+					continue
+				}
+				var rec OIDCProviderRecord
+				if err := json.Unmarshal(resp.Entry.Content, &rec); err != nil {
+					glog.Warningf("skipping malformed OIDC provider record %s: %v", resp.Entry.Name, err)
+					continue
+				}
+				out = append(out, &rec)
+			}
+			if pageCount < pageSize {
 				break
 			}
-			if resp.Entry == nil || resp.Entry.IsDirectory {
-				continue
-			}
-			if !strings.HasSuffix(resp.Entry.Name, ".json") {
-				continue
-			}
-			var rec OIDCProviderRecord
-			if err := json.Unmarshal(resp.Entry.Content, &rec); err != nil {
-				glog.Warningf("skipping malformed OIDC provider record %s: %v", resp.Entry.Name, err)
-				continue
-			}
-			out = append(out, &rec)
+			startFrom = lastName
 		}
 		return nil
 	})