[bucket] Fix s3manager endpoint mismatch with COSI credentials (#2211)

## What this PR does

Fixes s3manager UI deployment to use the actual S3 endpoint from
BucketInfo (COSI) instead of constructing it from the tenant namespace
host.

The deployment was using `s3.<tenant>.<cluster-domain>` while
credentials issued by COSI point to the root-level S3 endpoint. This
mismatch caused "invalid credentials" errors on login even with correct
credentials from the bucket secret.

Falls back to the constructed namespace host on first deploy before
BucketAccess secrets exist.

### Release note

```release-note
[bucket] Fix s3manager endpoint mismatch causing "invalid credentials" errors in login mode
```

<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->

## Summary by CodeRabbit

* **Refactor**
* Deployment configuration now supports per-user endpoint customization.
Endpoints are dynamically retrieved from account-specific settings,
enabling flexible configurations while maintaining backward
compatibility for standard deployments without custom settings.

<!-- end of auto-generated comment: release notes by coderabbit.ai -->

packages/system/bucket/templates/deployment.yaml

@@ -1,3 +1,12 @@
+{{- $endpoint := printf "s3.%s" .Values._namespace.host }}
+{{- range $name, $user := .Values.users }}
+  {{- $secretName := printf "%s-%s" $.Values.bucketName $name }}
+  {{- $existingSecret := lookup "v1" "Secret" $.Release.Namespace $secretName }}
+  {{- if $existingSecret }}
+    {{- $bucketInfo := fromJson (b64dec (index $existingSecret.data "BucketInfo")) }}
+    {{- $endpoint = trimPrefix "https://" (index $bucketInfo.spec.secretS3 "endpoint") }}
+  {{- end }}
+{{- end }}
 apiVersion: apps/v1
 kind: Deployment
 metadata:
@@ -17,6 +26,6 @@ spec:
         image: "{{ $.Files.Get "images/s3manager.tag" | trim }}"
         env:
         - name: ENDPOINT
-          value: "s3.{{ .Values._namespace.host }}"
+          value: {{ $endpoint | quote }}
         - name: SKIP_SSL_VERIFICATION
           value: "true"