feat(server): realtime notification & task status (#14934)

#### PR Dependency Tree


* **PR #14934** 👈

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**
* Full realtime platform added: live notifications, comments, embedding
progress, and transcription task updates via realtime subscriptions.

* **Chores**
* Frontend switched from polling/GraphQL queries to realtime channels;
legacy query fields marked deprecated and client libs updated to use
realtime APIs.

[![Review Change
Stack](https://storage.googleapis.com/coderabbit_public_assets/review-stack-in-coderabbit-ui.svg)](https://app.coderabbit.ai/change-stack/toeverything/AFFiNE/pull/14934)
<!-- end of auto-generated comment: release notes by coderabbit.ai -->


#### PR Dependency Tree


* **PR #14934** 👈
  * **PR #14936**

This tree was auto-generated by
[Charcoal](https://github.com/danerwilliams/charcoal)

packages/backend/server/package.json

@@ -114,6 +114,7 @@
     "@affine-tools/cli": "workspace:*",
     "@affine-tools/utils": "workspace:*",
     "@affine/graphql": "workspace:*",
+    "@affine/realtime": "workspace:*",
     "@faker-js/faker": "^10.1.0",
     "@nestjs/swagger": "^11.2.7",
     "@nestjs/testing": "patch:@nestjs/testing@npm%3A11.1.18#~/.yarn/patches/@nestjs-testing-npm-11.1.18-32c0f6af12.patch",