[refactor] Improve updates/notifications domain organization (#5590)

* [refactor] Move update-related functionality to platform/updates domain

Reorganizes release management, version compatibility, and notification functionality
following Domain-Driven Design principles, mirroring VSCode's architecture pattern.

- Move releaseService.ts to platform/updates/common/
- Move releaseStore.ts to platform/updates/common/
- Move versionCompatibilityStore.ts to platform/updates/common/
- Move useFrontendVersionMismatchWarning.ts to platform/updates/common/
- Move toastStore.ts to platform/updates/common/
- Move ReleaseNotificationToast.vue to platform/updates/components/
- Move WhatsNewPopup.vue to platform/updates/components/
- Update 25+ import paths across codebase and tests

This creates a cohesive "updates" domain containing all functionality related to
software updates, version checking, release notifications, and user communication
about application state changes.

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

* fix imports

---------

Co-authored-by: Claude <noreply@anthropic.com>

tests-ui/tests/services/releaseService.test.ts

@@ -1,7 +1,7 @@
 import axios from 'axios'
 import { beforeEach, describe, expect, it, vi } from 'vitest'
 
-import { useReleaseService } from '@/services/releaseService'
+import { useReleaseService } from '@/platform/updates/common/releaseService'
 
 // Hoist the mock to avoid hoisting issues
 const mockAxiosInstance = vi.hoisted(() => ({