feat(server): add image resize support (#14588)

fix #13842 


#### PR Dependency Tree


* **PR #14588** 👈

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**
* Images are now processed natively and converted to WebP for smaller,
optimized files; Copilot and avatar attachments use the processed WebP
output.
* Avatar uploads accept BMP, GIF, JPEG, PNG, WebP (5MB max) and are
downscaled to a standard edge.

* **Error Messages / i18n**
  * Added localized error "Image format not supported: {format}".

* **Tests**
* Added end-to-end and unit tests for conversion, EXIF preservation, and
upload limits.

* **Chores**
  * Added native image-processing dependencies.
<!-- end of auto-generated comment: release notes by coderabbit.ai -->

packages/backend/native/Cargo.toml

@@ -14,9 +14,13 @@ affine_common = { workspace = true, features = [
   "napi",
   "ydoc-loader",
 ] }
+anyhow = { workspace = true }
 chrono = { workspace = true }
 file-format = { workspace = true }
+image = { workspace = true }
 infer = { workspace = true }
+libwebp-sys = { workspace = true }
+little_exif = { workspace = true }
 llm_adapter = { workspace = true }
 mp4parse = { workspace = true }
 napi = { workspace = true, features = ["async"] }