feat(core): add ai file context api (#10842)

Close [BS-2349](https://linear.app/affine-design/issue/BS-2349).

### What Changed?
- Add file context graphql apis
- Pass matched file chunks to LLM

[录屏2025-02-19 23.27.47.mov <span class="graphite__hidden">(uploaded via Graphite)</span> <img class="graphite__hidden" src="https://app.graphite.dev/api/v1/graphite/video/thumbnail/sJGviKxfE3Ap685cl5bj/8e8a98ca-6959-4bb6-9759-b51d97cede49.mov" />](https://app.graphite.dev/media/video/sJGviKxfE3Ap685cl5bj/8e8a98ca-6959-4bb6-9759-b51d97cede49.mov)

blocksuite/affine/shared/src/services/file-size-limit-service.ts

@@ -1,7 +1,7 @@
 import { StoreExtension } from '@blocksuite/store';
 
 // bytes.parse('2GB')
-const maxFileSize = 2147483648;
+const maxFileSize = 2 * 1024 * 1024 * 1024;
 
 export class FileSizeLimitService extends StoreExtension {
   static override key = 'file-size-limit';