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/components/helpcenter/HelpCenterMenuContent.vue

@@ -159,13 +159,13 @@ import { useI18n } from 'vue-i18n'
 
 import PuzzleIcon from '@/components/icons/PuzzleIcon.vue'
 import { useExternalLink } from '@/composables/useExternalLink'
-import { isCloud } from '@/platform/distribution/types'
+import { isCloud, isDesktop } from '@/platform/distribution/types'
 import { useSettingStore } from '@/platform/settings/settingStore'
 import { useTelemetry } from '@/platform/telemetry'
 import type { ReleaseNote } from '@/platform/updates/common/releaseService'
 import { useReleaseStore } from '@/platform/updates/common/releaseStore'
 import { useCommandStore } from '@/stores/commandStore'
-import { electronAPI, isElectron } from '@/utils/envUtil'
+import { electronAPI } from '@/utils/envUtil'
 import { formatVersionAnchor } from '@/utils/formatUtil'
 import { useConflictAcknowledgment } from '@/workbench/extensions/manager/composables/useConflictAcknowledgment'
 import { useManagerState } from '@/workbench/extensions/manager/composables/useManagerState'
@@ -241,7 +241,7 @@ const moreItems = computed<MenuItem[]>(() => {
       key: 'desktop-guide',
       type: 'item',
       label: t('helpCenter.desktopUserGuide'),
-      visible: isElectron(),
+      visible: isDesktop,
       action: () => {
         trackResourceClick('docs', true)
         openExternalLink(
@@ -257,7 +257,7 @@ const moreItems = computed<MenuItem[]>(() => {
       key: 'dev-tools',
       type: 'item',
       label: t('helpCenter.openDevTools'),
-      visible: isElectron(),
+      visible: isDesktop,
       action: () => {
         openDevTools()
         emit('close')
@@ -266,13 +266,13 @@ const moreItems = computed<MenuItem[]>(() => {
     {
       key: 'divider-1',
       type: 'divider',
-      visible: isElectron()
+      visible: isDesktop
     },
     {
       key: 'reinstall',
       type: 'item',
       label: t('helpCenter.reinstall'),
-      visible: isElectron(),
+      visible: isDesktop,
       action: () => {
         onReinstall()
         emit('close')
@@ -374,7 +374,7 @@ const menuItems = computed<MenuItem[]>(() => {
     })
   }
   // Update ComfyUI - only for non-desktop, non-cloud with new manager UI
-  if (!isElectron() && !isCloud && isNewManagerUI.value) {
+  if (!isDesktop && !isCloud && isNewManagerUI.value) {
     items.push({
       key: 'update-comfyui',
       type: 'item',
@@ -551,13 +551,13 @@ const onSubmenuLeave = (): void => {
 }
 
 const openDevTools = (): void => {
-  if (isElectron()) {
+  if (isDesktop) {
     electronAPI().openDevTools()
   }
 }
 
 const onReinstall = (): void => {
-  if (isElectron()) {
+  if (isDesktop) {
     void electronAPI().reinstall()
   }
 }