feat(server): impl storage runtime (#15181)

#### PR Dependency Tree


* **PR #15181** 👈

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 an additional storage backend option: asset-pack based storage
(provider for avatar, blob, and copilot).
* Introduced a dedicated storage runtime with provider capability
reporting and expanded object operations (put/head/get/list/delete),
including presigned and multipart flows where supported.
* Cloudflare R2 `jurisdiction` now uses an explicit default when
omitted.
* **Bug Fixes**
  * Broadened avatar access to allow both fs and asset-pack providers.
* Improved workspace blob upload completion validation and handling when
stored objects are missing or mismatched.
<!-- end of auto-generated comment: release notes by coderabbit.ai -->

packages/backend/native/src/utils.rs

@@ -1,3 +1,9 @@
+use std::time::{SystemTime, SystemTimeError, UNIX_EPOCH};
+
+pub(crate) fn system_time_millis(time: SystemTime) -> Result<u128, SystemTimeError> {
+  Ok(time.duration_since(UNIX_EPOCH)?.as_millis())
+}
+
 fn collapse_whitespace(s: &str) -> String {
   let mut result = String::new();
   let mut prev_was_whitespace = false;