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/src/plugins/copilot/tools/doc-compose.ts

@@ -1,8 +1,8 @@
 import { Logger } from '@nestjs/common';
-import { tool } from 'ai';
 import { z } from 'zod';
 
 import { toolError } from './error';
+import { defineTool } from './tool';
 import type { CopilotProviderFactory, PromptService } from './types';
 
 const logger = new Logger('DocComposeTool');
@@ -11,7 +11,7 @@ export const createDocComposeTool = (
   promptService: PromptService,
   factory: CopilotProviderFactory
 ) => {
-  return tool({
+  return defineTool({
     description:
       'Write a new document with markdown content. This tool creates structured markdown content for documents including titles, sections, and formatting.',
     inputSchema: z.object({