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 -->

Cargo.toml

@@ -40,10 +40,19 @@ resolver = "3"
   dotenvy = "0.15"
   file-format = { version = "0.28", features = ["reader"] }
   homedir = "0.3"
+  image = { version = "0.25.9", default-features = false, features = [
+    "bmp",
+    "gif",
+    "jpeg",
+    "png",
+    "webp",
+  ] }
   infer = { version = "0.19.0" }
   lasso = { version = "0.7", features = ["multi-threaded"] }
   lib0 = { version = "0.16", features = ["lib0-serde"] }
   libc = "0.2"
+  libwebp-sys = "0.14.2"
+  little_exif = "0.6.23"
   llm_adapter = "0.1.1"
   log = "0.4"
   loom = { version = "0.7", features = ["checkpoint"] }