[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/store/versionCompatibilityStore.test.ts

@@ -2,8 +2,8 @@ import { createPinia, setActivePinia } from 'pinia'
 import { afterEach, beforeEach, describe, expect, it, vi } from 'vitest'
 import { ref } from 'vue'
 
+import { useVersionCompatibilityStore } from '@/platform/updates/common/versionCompatibilityStore'
 import { useSystemStatsStore } from '@/stores/systemStatsStore'
-import { useVersionCompatibilityStore } from '@/stores/versionCompatibilityStore'
 
 vi.mock('@/config', () => ({
   default: {