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 -->

packages/backend/server/package.json

@@ -25,8 +25,6 @@
   "dependencies": {
     "@affine/s3-compat": "workspace:*",
     "@affine/server-native": "workspace:*",
-    "@ai-sdk/google": "^3.0.46",
-    "@ai-sdk/google-vertex": "^4.0.83",
     "@apollo/server": "^4.13.0",
     "@fal-ai/serverless-client": "^0.15.0",
     "@google-cloud/opentelemetry-cloud-trace-exporter": "^3.0.0",
@@ -66,7 +64,6 @@
     "@queuedash/api": "^3.16.0",
     "@react-email/components": "^0.5.7",
     "@socket.io/redis-adapter": "^8.3.0",
-    "ai": "^6.0.118",
     "bullmq": "^5.40.2",
     "cookie-parser": "^1.4.7",
     "cross-env": "^10.1.0",