[refactor] Unify Cloud/OSS Missing Nodes modal (#6673)

## Summary
- Merged separate Cloud and OSS workflow warning modals into single
unified modal
- Removed legacy LoadWorkflowWarning.vue
- Renamed CloudMissingNodes* components to MissingNodes* for clarity
- Environment branching now handled internally via isCloud flag
- Restructured i18n: removed loadWorkflowWarning, added
missingNodes.cloud/oss sections
- Improved OSS button styling to match Cloud consistency

## Key Changes
- **OSS**: "Open Manager" + "Install All" buttons
- **Cloud**: "Learn More" + "Got It" buttons (unchanged)
- Single unified modal displays different UI/text based on environment

## 📝 Note on File Renames

This PR renames the following files:

- `CloudMissingNodesHeader.vue` → `MissingNodesHeader.vue` (R053, 53%
similarity)
- `CloudMissingNodesContent.vue` → `MissingNodesContent.vue` (R067, 67%
similarity)
- `LoadWorkflowWarning.vue` → `MissingNodesFooter.vue` (R051, 51%
similarity)
- `CloudMissingNodesFooter.vue` → Deleted (replaced by new
MissingNodesFooter)

**Why GitHub PR UI doesn't show renames properly:**

GitHub detects renames only when file similarity is above 70%. In this
PR, the Cloud/OSS unification significantly modified file contents,
resulting in 51-67% similarity.

However, **Git history correctly records these as renames**. You can
verify with:

```bash
git show <commit-hash> --name-status
```

While GitHub UI shows "additions/deletions", these are actually rename +
modification operations.

## Test Plan
- [x] Test OSS mode: missing nodes modal shows "Open Manager" and
"Install All" buttons
- [x] Test Cloud mode: missing nodes modal shows "Learn More" and "Got
It" buttons
- [x] Verify Install All button functionality in OSS
- [x] Verify modal closes automatically after all nodes are installed
(OSS)


[missingnodes.webm](https://github.com/user-attachments/assets/36d3b4b0-ff8b-4b45-824c-3bc15d93f1a2)

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

┆Issue is synchronized with this [Notion
page](https://www.notion.so/PR-6673-refactor-Unify-Cloud-OSS-Missing-Nodes-modal-2aa6d73d365081a88827d0fa85db4c63)
by [Unito](https://www.unito.io)

---------

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

src/scripts/app.ts

@@ -1018,11 +1018,7 @@ export class ComfyApp {
 
   private showMissingNodesError(missingNodeTypes: MissingNodeType[]) {
     if (useSettingStore().get('Comfy.Workflow.ShowMissingNodesWarning')) {
-      if (isCloud) {
-        useDialogService().showCloudLoadWorkflowWarning({ missingNodeTypes })
-      } else {
-        useDialogService().showLoadWorkflowWarning({ missingNodeTypes })
-      }
+      useDialogService().showLoadWorkflowWarning({ missingNodeTypes })
     }
   }