feat(server): migrate copilot to native (#14620)

#### PR Dependency Tree


* **PR #14620** 👈

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**
* Native LLM workflows: structured outputs, embeddings, and reranking
plus richer multimodal attachments (images, audio, files) and improved
remote-attachment inlining.

* **Refactor**
* Tooling API unified behind a local tool-definition helper;
provider/adapters reorganized to route through native dispatch paths.

* **Chores**
* Dependency updates, removed legacy Google SDK integrations, and
increased front memory allocation.

* **Tests**
* Expanded end-to-end and streaming tests exercising native provider
flows, attachments, and rerank/structured scenarios.
<!-- end of auto-generated comment: release notes by coderabbit.ai -->

Cargo.toml

@@ -53,10 +53,11 @@ resolver = "3"
   libc = "0.2"
   libwebp-sys = "0.14.2"
   little_exif = "0.6.23"
-  llm_adapter = "0.1.1"
+  llm_adapter = { version = "0.1.3", default-features = false }
   log = "0.4"
   loom = { version = "0.7", features = ["checkpoint"] }
   lru = "0.16"
+  matroska = "0.30"
   memory-indexer = "0.3.0"
   mimalloc = "0.1"
   mp4parse = "0.17"