Update desktop docs to platform-specific URLs (#5757)

Fixes #5751

## Summary
- Replaces outdated Notion link with docs.comfy.org URLs
- Uses Electron API to detect platform for Windows/macOS specific docs

┆Issue is synchronized with this [Notion
page](https://www.notion.so/PR-5757-Update-desktop-docs-to-platform-specific-URLs-2786d73d36508188a200ed3ad91b836f)
by [Unito](https://www.unito.io)

src/components/helpcenter/HelpCenterMenuContent.vue

@@ -168,7 +168,8 @@ const EXTERNAL_LINKS = {
   DOCS: 'https://docs.comfy.org/',
   DISCORD: 'https://www.comfy.org/discord',
   GITHUB: 'https://github.com/comfyanonymous/ComfyUI',
-  DESKTOP_GUIDE: 'https://comfyorg.notion.site/',
+  DESKTOP_GUIDE_WINDOWS: 'https://docs.comfy.org/installation/desktop/windows',
+  DESKTOP_GUIDE_MACOS: 'https://docs.comfy.org/installation/desktop/macos',
   UPDATE_GUIDE: 'https://docs.comfy.org/installation/update_comfyui'
 } as const
 
@@ -222,7 +223,11 @@ const moreItems = computed<MenuItem[]>(() => {
       label: t('helpCenter.desktopUserGuide'),
       visible: isElectron(),
       action: () => {
-        openExternalLink(EXTERNAL_LINKS.DESKTOP_GUIDE)
+        const docsUrl =
+          electronAPI().getPlatform() === 'darwin'
+            ? EXTERNAL_LINKS.DESKTOP_GUIDE_MACOS
+            : EXTERNAL_LINKS.DESKTOP_GUIDE_WINDOWS
+        openExternalLink(docsUrl)
         emit('close')
       }
     },

src/extensions/core/electronAdapter.ts

@@ -9,6 +9,12 @@ import { useDialogService } from '@/services/dialogService'
 import { electronAPI as getElectronAPI, isElectron } from '@/utils/envUtil'
 import { checkMirrorReachable } from '@/utils/networkUtil'
 
+// Desktop documentation URLs
+const DESKTOP_DOCS = {
+  WINDOWS: 'https://docs.comfy.org/installation/desktop/windows',
+  MACOS: 'https://docs.comfy.org/installation/desktop/macos'
+} as const
+
 ;(async () => {
   if (!isElectron()) return
 
@@ -159,7 +165,11 @@ import { checkMirrorReachable } from '@/utils/networkUtil'
         label: 'Desktop User Guide',
         icon: 'pi pi-book',
         function() {
-          window.open('https://comfyorg.notion.site/', '_blank')
+          const docsUrl =
+            electronAPI.getPlatform() === 'darwin'
+              ? DESKTOP_DOCS.MACOS
+              : DESKTOP_DOCS.WINDOWS
+          window.open(docsUrl, '_blank')
         }
       },
       {