feat: surface missing models in Error Tab for OSS and remove legacy dialog (#9921)

## Summary
- Surface missing models in the Error Tab for OSS environments,
replacing the legacy modal dialog
- Add Download button per model and Download All button in group header
with file size display
- Move download business logic from `components/dialog/content` to
`platform/missingModel`
- Remove legacy missing models dialog components and composable

## Changes
- **Pipeline**: Remove `isCloud` guard from `scanAllModelCandidates` and
`surfaceMissingModels` so OSS detects missing models
- **Grouping**: Group non-asset-supported models by directory in OSS
instead of lumping into UNSUPPORTED
- **UI**: Add Download button (matching Install Node Pack design) and
Download All header button
- **Store**: Add `folderPaths`/`fileSizes` state with setter methods,
race condition guard
- **Cleanup**: Delete `MissingModelsContent`, `MissingModelsHeader`,
`MissingModelsFooter`, `useMissingModelsDialog`, `missingModelsUtils`
- **Tests**: Add OSS/Cloud grouping tests, migrate Playwright E2E to
Error Tab, improve test isolation
- **Snapshots**: Reset Playwright screenshot expectations since OSS
missing model error detection now causes red highlights on affected
nodes
- **Accessibility**: Add `aria-label` with model name, `aria-expanded`
on toggle, warning icon for unknown category

## Test plan
- [x] Unit tests pass (86 tests)
- [x] TypeScript typecheck passes
- [x] knip passes
- [x] Load workflow with missing models in OSS → Error Tab shows missing
models grouped by directory
- [x] Download button triggers browser download with correct URL
- [x] Download All button downloads all downloadable models
- [x] Cloud environment behavior unchanged
- [x] Playwright E2E: `pnpm test:browser:local -- --grep "Missing models
in Error Tab"`

## Screenshots


https://github.com/user-attachments/assets/12f15e09-215a-4c58-87ed-39bbffd1359c

 


┆Issue is synchronized with this [Notion
page](https://www.notion.so/PR-9921-feat-surface-missing-models-in-Error-Tab-for-OSS-and-remove-legacy-dialog-3236d73d365081f0a9dfc291978f5ecf)
by [Unito](https://www.unito.io)

---------

Co-authored-by: GitHub Action <action@github.com>
Co-authored-by: github-actions <github-actions@github.com>

src/platform/missingModel/missingModelStore.ts

@@ -84,6 +84,8 @@ export const useMissingModelStore = defineStore('missingModel', () => {
   const urlFetching = ref<Record<string, boolean>>({})
   const urlErrors = ref<Record<string, string>>({})
   const urlImporting = ref<Record<string, boolean>>({})
+  const folderPaths = ref<Record<string, string[]>>({})
+  const fileSizes = ref<Record<string, number>>({})
 
   const _urlDebounceTimers: Record<string, ReturnType<typeof setTimeout>> = {}
 
@@ -162,6 +164,14 @@ export const useMissingModelStore = defineStore('missingModel', () => {
     }
   }
 
+  function setFolderPaths(paths: Record<string, string[]>) {
+    folderPaths.value = paths
+  }
+
+  function setFileSize(url: string, size: number) {
+    fileSizes.value[url] = size
+  }
+
   function clearMissingModels() {
     _verificationAbortController?.abort()
     _verificationAbortController = null
@@ -176,6 +186,8 @@ export const useMissingModelStore = defineStore('missingModel', () => {
     urlFetching.value = {}
     urlErrors.value = {}
     urlImporting.value = {}
+    folderPaths.value = {}
+    fileSizes.value = {}
   }
 
   return {
@@ -205,6 +217,11 @@ export const useMissingModelStore = defineStore('missingModel', () => {
     urlFetching,
     urlErrors,
     urlImporting,
+    folderPaths,
+    fileSizes,
+
+    setFolderPaths,
+    setFileSize,
 
     setDebounceTimer,
     clearDebounceTimer