feat(server): blob reconciliation (#15165)

#### PR Dependency Tree


* **PR #15165** 👈

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 automated backend maintenance for missing blob metadata
backfill, document-to-blob reference rebuilding, and unreferenced blob
cleanup planning/execution.
* Introduced scheduled batch processing (workspace-paged) and paginated
object-storage listing.
* **Bug Fixes**
* Improved reliability of object-storage reads by treating expected “not
found” results as non-errors.
* Strengthened blob/expired cleanup flows with runtime-driven batching
and reduced coupling to metadata synchronization.
* **Tests**
* Expanded unit and e2e coverage for partial blob metadata and updated
runtime/job cleanup test assertions.
<!-- end of auto-generated comment: release notes by coderabbit.ai -->

.docker/selfhost/schema.json

@@ -121,6 +121,18 @@
           "default": {
             "concurrency": 1
           }
+        },
+        "queues.backendRuntime": {
+          "type": "object",
+          "description": "The config for backend runtime job queue\n@default {\"concurrency\":1}",
+          "properties": {
+            "concurrency": {
+              "type": "number"
+            }
+          },
+          "default": {
+            "concurrency": 1
+          }
         }
       }
     },