[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/MissingModelUrlInput.vue

@@ -0,0 +1,156 @@
+<template>
+  <div
+    :class="
+      cn(
+        'flex h-8 items-center rounded-lg border border-transparent bg-secondary-background px-3 transition-colors focus-within:border-interface-stroke',
+        !canImportModels && 'cursor-pointer'
+      )
+    "
+    v-bind="upgradePromptAttrs"
+    @click="!canImportModels && showUploadDialog()"
+  >
+    <label :for="`url-input-${modelKey}`" class="sr-only">
+      {{ t('rightSidePanel.missingModels.urlPlaceholder') }}
+    </label>
+    <input
+      :id="`url-input-${modelKey}`"
+      type="text"
+      :value="urlInputs[modelKey] ?? ''"
+      :readonly="!canImportModels"
+      :placeholder="t('rightSidePanel.missingModels.urlPlaceholder')"
+      :class="
+        cn(
+          'text-foreground w-full border-none bg-transparent text-xs outline-none placeholder:text-muted-foreground',
+          !canImportModels && 'pointer-events-none opacity-60'
+        )
+      "
+      @input="
+        handleUrlInput(modelKey, ($event.target as HTMLInputElement).value)
+      "
+    />
+    <Button
+      v-if="urlInputs[modelKey]"
+      variant="textonly"
+      size="icon-sm"
+      :aria-label="t('rightSidePanel.missingModels.clearUrl')"
+      class="ml-1 shrink-0"
+      @click.stop="handleUrlInput(modelKey, '')"
+    >
+      <i aria-hidden="true" class="icon-[lucide--x] size-3.5" />
+    </Button>
+  </div>
+
+  <TransitionCollapse>
+    <div v-if="urlMetadata[modelKey]" class="flex flex-col gap-2">
+      <div class="flex items-center gap-2 px-0.5 pt-0.5">
+        <span class="text-foreground min-w-0 truncate text-xs font-bold">
+          {{ urlMetadata[modelKey]?.filename }}
+        </span>
+        <span
+          v-if="(urlMetadata[modelKey]?.content_length ?? 0) > 0"
+          class="shrink-0 rounded-sm bg-secondary-background-selected px-1.5 py-0.5 text-xs font-medium text-muted-foreground"
+        >
+          {{ formatSize(urlMetadata[modelKey]?.content_length ?? 0) }}
+        </span>
+      </div>
+
+      <div v-if="typeMismatch" class="flex items-start gap-1.5 px-0.5">
+        <i
+          aria-hidden="true"
+          class="mt-0.5 icon-[lucide--triangle-alert] size-3 shrink-0 text-warning-background"
+        />
+        <span class="text-xs/tight text-warning-background">
+          {{
+            t('rightSidePanel.missingModels.typeMismatch', {
+              detectedType: typeMismatch
+            })
+          }}
+        </span>
+      </div>
+
+      <div class="pt-0.5">
+        <Button
+          variant="primary"
+          class="h-9 w-full justify-center gap-2 text-sm font-semibold"
+          :loading="urlImporting[modelKey]"
+          @click="handleImport(modelKey, directory)"
+        >
+          <i aria-hidden="true" class="icon-[lucide--download] size-4" />
+          {{
+            typeMismatch
+              ? t('rightSidePanel.missingModels.importAnyway')
+              : t('rightSidePanel.missingModels.import')
+          }}
+        </Button>
+      </div>
+    </div>
+  </TransitionCollapse>
+
+  <TransitionCollapse>
+    <div
+      v-if="urlFetching[modelKey]"
+      aria-live="polite"
+      class="flex items-center justify-center py-2"
+    >
+      <i
+        aria-hidden="true"
+        class="icon-[lucide--loader-circle] size-4 animate-spin text-muted-foreground"
+      />
+      <span class="sr-only">{{ t('g.loading') }}</span>
+    </div>
+  </TransitionCollapse>
+
+  <TransitionCollapse>
+    <div v-if="urlErrors[modelKey]" class="px-0.5" role="alert">
+      <span class="text-xs text-destructive-background-hover">
+        {{ urlErrors[modelKey] }}
+      </span>
+    </div>
+  </TransitionCollapse>
+</template>
+
+<script setup lang="ts">
+import { computed } from 'vue'
+import { storeToRefs } from 'pinia'
+import { useI18n } from 'vue-i18n'
+import { cn } from '@/utils/tailwindUtil'
+import Button from '@/components/ui/button/Button.vue'
+import TransitionCollapse from '@/components/rightSidePanel/layout/TransitionCollapse.vue'
+import { formatSize } from '@/utils/formatUtil'
+import { useMissingModelStore } from '@/platform/missingModel/missingModelStore'
+import { useMissingModelInteractions } from '@/platform/missingModel/composables/useMissingModelInteractions'
+import { useFeatureFlags } from '@/composables/useFeatureFlags'
+import { useModelUpload } from '@/platform/assets/composables/useModelUpload'
+
+const { modelKey, directory, typeMismatch } = defineProps<{
+  modelKey: string
+  directory: string | null
+  typeMismatch: string | null
+}>()
+
+const { t } = useI18n()
+const { flags } = useFeatureFlags()
+const canImportModels = computed(() => flags.privateModelsEnabled)
+const { showUploadDialog } = useModelUpload()
+
+const store = useMissingModelStore()
+const { urlInputs, urlMetadata, urlFetching, urlErrors, urlImporting } =
+  storeToRefs(store)
+
+const { handleUrlInput, handleImport } = useMissingModelInteractions()
+
+const upgradePromptAttrs = computed(() =>
+  canImportModels.value
+    ? {}
+    : {
+        role: 'button',
+        tabindex: 0,
+        onKeydown: (e: KeyboardEvent) => {
+          if (e.key === 'Enter' || e.key === ' ') {
+            e.preventDefault()
+            showUploadDialog()
+          }
+        }
+      }
+)
+</script>