feat(core): add google vertex ai (#12423)

Close [AI-125](https://linear.app/affine-design/issue/AI-125)

<!-- This is an auto-generated comment: release notes by coderabbit.ai -->
## Summary by CodeRabbit

- **New Features**
  - Added new provider configurations `geminiVertex` and `anthropicVertex` for Google Vertex AI in backend schema, provider classes, and admin config.
  - Introduced `GeminiVertexProvider` and `AnthropicVertexProvider` classes supporting Vertex AI models with specific capabilities.
  - Expanded model options for transcription prompts with newer Gemini models.
  - Re-exported provider modules to include Vertex AI variants.

- **Improvements**
  - Extended provider architecture to support separate Vertex AI configurations and models.
  - Updated test setup to replace deprecated provider references with new Vertex variants.
  - Consolidated environment variables for server testing with a single `SERVER_CONFIG`.

- **Bug Fixes**
  - Updated mock models and import references in tests to align with new provider classes.

- **Chores**
  - Added `@ai-sdk/google-vertex` dependency for Vertex AI support.
  - Updated dependency list to include `@ai-sdk/google-vertex`.

<!-- end of auto-generated comment: release notes by coderabbit.ai -->

packages/backend/server/src/__tests__/copilot.e2e.ts

@@ -19,7 +19,7 @@ import { MockEmbeddingClient } from '../plugins/copilot/context/embedding';
 import { prompts, PromptService } from '../plugins/copilot/prompt';
 import {
   CopilotProviderFactory,
-  GeminiProvider,
+  GeminiGenerativeProvider,
   OpenAIProvider,
 } from '../plugins/copilot/providers';
 import { CopilotStorage } from '../plugins/copilot/storage';
@@ -100,7 +100,9 @@ test.before(async t => {
         },
       });
       m.overrideProvider(OpenAIProvider).useClass(MockCopilotProvider);
-      m.overrideProvider(GeminiProvider).useClass(MockCopilotProvider);
+      m.overrideProvider(GeminiGenerativeProvider).useClass(
+        MockCopilotProvider
+      );
     },
   });
 
@@ -935,8 +937,8 @@ test('should be able to transcript', async t => {
   const { id: workspaceId } = await createWorkspace(app);
 
   for (const [provider, func] of [
-    [GeminiProvider, 'text'],
-    [GeminiProvider, 'structure'],
+    [GeminiGenerativeProvider, 'text'],
+    [GeminiGenerativeProvider, 'structure'],
   ] as const) {
     Sinon.stub(app.get(provider), func).resolves(
       JSON.stringify([

packages/backend/server/src/__tests__/mocks/copilot.mock.ts

@@ -111,7 +111,7 @@ export class MockCopilotProvider extends OpenAIProvider {
       ],
     },
     {
-      id: 'gemini-2.5-pro-preview-05-06',
+      id: 'gemini-2.5-flash-preview-05-20',
       capabilities: [
         {
           input: [ModelInputType.Text, ModelInputType.Image],