chore(server): add comment attachment storage metrics (#13143)

close AF-2728



#### PR Dependency Tree


* **PR #13143** 👈

This tree was auto-generated by
[Charcoal](https://github.com/danerwilliams/charcoal)

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

## Summary by CodeRabbit

* **New Features**
* Added metrics tracking for comment attachment uploads, including
recording attachment size and total uploads by MIME type.
* Enhanced logging for attachment uploads with detailed information such
as workspace ID, document ID, file size, and user ID.

* **Chores**
* Expanded internal metric categories to include storage-related
metrics.

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

packages/backend/server/src/base/metrics/metrics.ts

@@ -59,7 +59,8 @@ export type KnownMetricScopes =
   | 'mail'
   | 'ai'
   | 'event'
-  | 'queue';
+  | 'queue'
+  | 'storage';
 
 const metricCreators: MetricCreators = {
   counter(meter: Meter, name: string, opts?: MetricOptions) {

packages/backend/server/src/core/storage/wrappers/comment-attachment.ts

@@ -4,6 +4,7 @@ import {
   autoMetadata,
   Config,
   EventBus,
+  metrics,
   OnEvent,
   type StorageProvider,
   StorageProviderFactory,
@@ -69,15 +70,23 @@ export class CommentAttachmentStorage {
       blob,
       meta
     );
+    const mime = meta.contentType ?? 'application/octet-stream';
+    const size = blob.length;
     await this.models.commentAttachment.upsert({
       workspaceId,
       docId,
       key,
       name,
-      mime: meta.contentType ?? 'application/octet-stream',
+      mime,
-      size: blob.length,
+      size,
       createdBy: userId,
     });
+
+    metrics.storage.histogram('comment_attachment_size').record(size, { mime });
+    metrics.storage.counter('comment_attachment_total').add(1, { mime });
+    this.logger.log(
+      `uploaded comment attachment ${workspaceId}/${docId}/${key} with size ${size}, mime: ${mime}, name: ${name}, user: ${userId}`
+    );
   }
 
   async get(