refactor: replace runtime isElectron() with build-time isDesktop constant (#8710)

## Summary

Replace all runtime `isElectron()` function calls with the build-time
`isDesktop` constant from `@/platform/distribution/types`, enabling
dead-code elimination in non-desktop builds.

## Changes

- **What**: Migrate 30 files from runtime `isElectron()` detection
(checking `window.electronAPI`) to the compile-time `isDesktop` constant
(driven by `__DISTRIBUTION__` Vite define). Remove `isElectron` from
`envUtil.ts`. Update `isNativeWindow()` to use `isDesktop`. Guard
`electronAPI()` calls behind `isDesktop` checks in stores. Update 7 test
files to use `vi.hoisted` + getter mock pattern for per-test `isDesktop`
toggling. Add `DISTRIBUTION=desktop` to `dev:electron` script.

## Review Focus

- The `electronDownloadStore.ts` now guards the top-level
`electronAPI()` call behind `isDesktop` to prevent crashes on
non-desktop builds.
- Test mocking pattern uses `vi.hoisted` with a getter to allow per-test
toggling of the `isDesktop` value.
- Pre-existing issues not addressed: `as ElectronAPI` cast in
`envUtil.ts`, `:class="[]"` in `BaseViewTemplate.vue`,
`@ts-expect-error` in `ModelLibrarySidebarTab.vue`.
- This subsumes PR #8627 and renders PR #6122 and PR #7374 obsolete.

┆Issue is synchronized with this [Notion
page](https://www.notion.so/PR-8710-refactor-replace-runtime-isElectron-with-build-time-isDesktop-constant-3006d73d365081c08037f0e61c2f6c77)
by [Unito](https://www.unito.io)

src/composables/sidebarTabs/useModelLibrarySidebarTab.ts

@@ -1,9 +1,9 @@
 import { markRaw } from 'vue'
 
 import ModelLibrarySidebarTab from '@/components/sidebar/tabs/ModelLibrarySidebarTab.vue'
+import { isDesktop } from '@/platform/distribution/types'
 import { useElectronDownloadStore } from '@/stores/electronDownloadStore'
 import type { SidebarTabExtension } from '@/types/extensionTypes'
-import { isElectron } from '@/utils/envUtil'
 
 export const useModelLibrarySidebarTab = (): SidebarTabExtension => {
   return {
@@ -15,7 +15,7 @@ export const useModelLibrarySidebarTab = (): SidebarTabExtension => {
     component: markRaw(ModelLibrarySidebarTab),
     type: 'vue',
     iconBadge: () => {
-      if (isElectron()) {
+      if (isDesktop) {
         const electronDownloadStore = useElectronDownloadStore()
         if (electronDownloadStore.inProgressDownloads.length > 0) {
           return electronDownloadStore.inProgressDownloads.length.toString()

src/composables/useExternalLink.test.ts

@@ -1,8 +1,15 @@
 import { beforeEach, describe, expect, it, vi } from 'vitest'
 
+const mockData = vi.hoisted(() => ({ isDesktop: false }))
+
+vi.mock('@/platform/distribution/types', () => ({
+  get isDesktop() {
+    return mockData.isDesktop
+  }
+}))
+
 // Mock the environment utilities
 vi.mock('@/utils/envUtil', () => ({
-  isElectron: vi.fn(),
   electronAPI: vi.fn()
 }))
 
@@ -20,14 +27,14 @@ vi.mock('@/i18n', () => ({
 
 // Import after mocking to get the mocked versions
 import { useExternalLink } from '@/composables/useExternalLink'
-import { electronAPI, isElectron } from '@/utils/envUtil'
+import { electronAPI } from '@/utils/envUtil'
 
 describe('useExternalLink', () => {
   beforeEach(() => {
     vi.clearAllMocks()
     // Reset to default state
     i18n.global.locale.value = 'en'
-    vi.mocked(isElectron).mockReturnValue(false)
+    mockData.isDesktop = false
   })
 
   describe('staticUrls', () => {
@@ -95,7 +102,7 @@ describe('useExternalLink', () => {
 
     it('should add platform suffix when requested', () => {
       i18n.global.locale.value = 'en'
-      vi.mocked(isElectron).mockReturnValue(true)
+      mockData.isDesktop = true
       vi.mocked(electronAPI).mockReturnValue({
         getPlatform: () => 'darwin'
       } as ReturnType<typeof electronAPI>)
@@ -107,7 +114,7 @@ describe('useExternalLink', () => {
 
     it('should add platform suffix with trailing slash', () => {
       i18n.global.locale.value = 'en'
-      vi.mocked(isElectron).mockReturnValue(true)
+      mockData.isDesktop = true
       vi.mocked(electronAPI).mockReturnValue({
         getPlatform: () => 'win32'
       } as ReturnType<typeof electronAPI>)
@@ -119,7 +126,7 @@ describe('useExternalLink', () => {
 
     it('should combine locale and platform', () => {
       i18n.global.locale.value = 'zh'
-      vi.mocked(isElectron).mockReturnValue(true)
+      mockData.isDesktop = true
       vi.mocked(electronAPI).mockReturnValue({
         getPlatform: () => 'darwin'
       } as ReturnType<typeof electronAPI>)
@@ -136,7 +143,7 @@ describe('useExternalLink', () => {
 
     it('should not add platform when not desktop', () => {
       i18n.global.locale.value = 'en'
-      vi.mocked(isElectron).mockReturnValue(false)
+      mockData.isDesktop = false
 
       const { buildDocsUrl } = useExternalLink()
       const url = buildDocsUrl('/installation/desktop', { platform: true })

src/composables/useExternalLink.ts

@@ -1,6 +1,7 @@
 import { computed } from 'vue'
 
-import { electronAPI, isElectron } from '@/utils/envUtil'
+import { isDesktop } from '@/platform/distribution/types'
+import { electronAPI } from '@/utils/envUtil'
 import { i18n } from '@/i18n'
 
 /**
@@ -30,7 +31,7 @@ export function useExternalLink() {
   })
 
   const platform = computed(() => {
-    if (!isElectron()) {
+    if (!isDesktop) {
       return null
     }