[feat] Surface missing models in Errors tab (Cloud) (#9743)

## Summary
When a workflow is loaded with missing models, users currently have no
way to identify or resolve them from within the UI. This PR adds a full
missing-model detection and resolution pipeline that surfaces missing
models in the Errors tab, allowing users to install or import them
without leaving the editor.

## Changes

### Missing Model Detection
- Scan all COMBO widgets across root graph and subgraphs for model-like
filenames during workflow load
- Enrich candidates with embedded workflow metadata (url, hash,
directory) when available
- Verify asset-supported candidates against the asset store
asynchronously to confirm installation status
- Propagate missing model state to `executionErrorStore` alongside
existing node/prompt errors

### Errors Tab UI — Model Resolution
- Group missing models by directory (e.g. `checkpoints`, `loras`, `vae`)
with collapsible category cards
- Each model row displays:
  - Model name with copy-to-clipboard button
  - Expandable list of referencing nodes with locate-on-canvas button
- **Library selector**: Pick an alternative from the user's existing
models to substitute the missing model with one click
- **URL import**: Paste a Civitai or HuggingFace URL to import a model
directly; debounced metadata fetch shows filename and file size before
confirming; type-mismatch warnings (e.g. importing a LoRA into
checkpoints directory) are surfaced with an "Import Anyway" option
- **Upgrade prompt**: In cloud environment, free-tier subscribers are
shown an upgrade modal when attempting URL import
- Separate "Import Not Supported" section for custom-node models that
cannot be auto-resolved
- Status card with live download progress, completion, failure, and
category-mismatch states

### Canvas Integration
- Highlight nodes and widgets that reference missing models with error
indicators
- Propagate missing-model badges through subgraph containers so issues
are visible at every graph level

### Code Cleanup
- Simplify `surfacePendingWarnings` in workflowService, remove stale
widget-detected model merging logic
- Add `flattenWorkflowNodes` utility to workflowSchema for traversing
nested subgraph structures
- Extract `MissingModelUrlInput`, `MissingModelLibrarySelect`,
`MissingModelStatusCard` as focused single-responsibility components

## Testing
- Unit tests for scan pipeline (`missingModelScan.test.ts`): enrichment,
skip-installed, subgraph flattening
- Unit tests for store (`missingModelStore.test.ts`): state management,
removal helpers
- Unit tests for interactions (`useMissingModelInteractions.test.ts`):
combo select, URL input, import flow, library confirm
- Component tests for `MissingModelCard` and error grouping
(`useErrorGroups.test.ts`)
- Updated `workflowService.test.ts` and `workflowSchema.test.ts` for new
logic

## Review Focus
- Missing model scan + enrichment pipeline in `missingModelScan.ts`
- Interaction composable `useMissingModelInteractions.ts` — URL metadata
fetch, library install, upload fallback
- Store integration and canvas-level error propagation

## Screenshots 


https://github.com/user-attachments/assets/339a6d5b-93a3-43cd-98dd-0fb00681b66f



┆Issue is synchronized with this [Notion
page](https://www.notion.so/PR-9743-feat-Surface-missing-models-in-Errors-tab-Cloud-3206d73d365081678326d3a16c2165d8)
by [Unito](https://www.unito.io)

src/platform/missingModel/components/MissingModelStatusCard.vue

@@ -0,0 +1,108 @@
+<template>
+  <div
+    aria-live="polite"
+    class="bg-foreground/5 relative mt-1 overflow-hidden rounded-lg border border-interface-stroke p-2"
+  >
+    <!-- Progress bar fill -->
+    <div
+      v-if="isDownloadActive"
+      class="absolute inset-y-0 left-0 bg-primary/10 transition-all duration-200 ease-linear"
+      :style="{ width: (downloadStatus?.progress ?? 0) * 100 + '%' }"
+    />
+
+    <div class="relative z-10 flex items-center gap-2">
+      <div class="flex size-8 shrink-0 items-center justify-center">
+        <i
+          v-if="categoryMismatch"
+          aria-hidden="true"
+          class="mt-0.5 icon-[lucide--triangle-alert] size-5 text-warning-background"
+        />
+        <i
+          v-else-if="downloadStatus?.status === 'failed'"
+          aria-hidden="true"
+          class="icon-[lucide--circle-alert] size-5 text-destructive-background"
+        />
+        <i
+          v-else-if="downloadStatus?.status === 'completed'"
+          aria-hidden="true"
+          class="icon-[lucide--check-circle] size-5 text-success-background"
+        />
+        <i
+          v-else-if="isDownloadActive"
+          aria-hidden="true"
+          class="icon-[lucide--loader-circle] size-5 animate-spin text-muted-foreground"
+        />
+        <i
+          v-else
+          aria-hidden="true"
+          class="icon-[lucide--file-check] size-5 text-muted-foreground"
+        />
+      </div>
+
+      <div class="flex min-w-0 flex-1 flex-col justify-center">
+        <span class="text-foreground truncate text-xs/tight font-medium">
+          {{ modelName }}
+        </span>
+        <span class="mt-0.5 text-xs/tight text-muted-foreground">
+          <template v-if="categoryMismatch">
+            {{
+              t('rightSidePanel.missingModels.alreadyExistsInCategory', {
+                category: categoryMismatch
+              })
+            }}
+          </template>
+          <template v-else-if="isDownloadActive">
+            {{ t('rightSidePanel.missingModels.importing') }}
+            {{ Math.round((downloadStatus?.progress ?? 0) * 100) }}%
+          </template>
+          <template v-else-if="downloadStatus?.status === 'completed'">
+            {{ t('rightSidePanel.missingModels.imported') }}
+          </template>
+          <template v-else-if="downloadStatus?.status === 'failed'">
+            {{
+              downloadStatus?.error ||
+              t('rightSidePanel.missingModels.importFailed')
+            }}
+          </template>
+          <template v-else>
+            {{ t('rightSidePanel.missingModels.usingFromLibrary') }}
+          </template>
+        </span>
+      </div>
+
+      <Button
+        variant="textonly"
+        size="icon-sm"
+        :aria-label="t('rightSidePanel.missingModels.cancelSelection')"
+        class="relative z-10 size-6 shrink-0 text-muted-foreground hover:text-base-foreground"
+        @click="emit('cancel')"
+      >
+        <i aria-hidden="true" class="icon-[lucide--circle-x] size-4" />
+      </Button>
+    </div>
+  </div>
+</template>
+
+<script setup lang="ts">
+import { useI18n } from 'vue-i18n'
+import Button from '@/components/ui/button/Button.vue'
+import type { AssetDownload } from '@/stores/assetDownloadStore'
+
+const {
+  modelName,
+  isDownloadActive,
+  downloadStatus = null,
+  categoryMismatch = null
+} = defineProps<{
+  modelName: string
+  isDownloadActive: boolean
+  downloadStatus?: AssetDownload | null
+  categoryMismatch?: string | null
+}>()
+
+const emit = defineEmits<{
+  cancel: []
+}>()
+
+const { t } = useI18n()
+</script>