[refactor] Unify small modal dialog styles with showSmallLayoutDialog (#8834)

## Summary
Extract a shared `showSmallLayoutDialog` utility and move
dialog-specific logic into composables, unifying the duplicated `pt`
configurations across small modal dialogs.

## Changes
- **`showSmallLayoutDialog`**: Added to `dialogService.ts` with a single
unified `pt` config for all small modal dialogs (missing nodes, missing
models, import failed, node conflict)
- **Composables**: Extracted 4 dialog functions from `dialogService`
into dedicated composables following the `useSettingsDialog` /
`useModelSelectorDialog` pattern:
  - `useMissingNodesDialog`
  - `useMissingModelsDialog`
  - `useImportFailedNodeDialog`
  - `useNodeConflictDialog`
- Each composable uses direct imports, synchronous `show()`, `hide()`,
and a `DIALOG_KEY` constant
- Updated all call sites (`app.ts`, `useHelpCenter`, `PackEnableToggle`,
`PackInstallButton`, `useImportFailedDetection`)

## Review Focus
- Unified `pt` config removes minor style variations between dialogs —
intentional design unification

┆Issue is synchronized with this [Notion
page](https://www.notion.so/PR-8834-refactor-Unify-small-modal-dialog-styles-with-showSmallLayoutDialog-3056d73d365081b6963beffc0e5943bf)
by [Unito](https://www.unito.io)

---------

Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>
Co-authored-by: github-actions <github-actions@github.com>

src/scripts/app.ts

@@ -52,6 +52,7 @@ import {
 } from '@/scripts/domWidget'
 import { useDialogService } from '@/services/dialogService'
 import { useBillingContext } from '@/composables/billing/useBillingContext'
+import { useMissingNodesDialog } from '@/composables/useMissingNodesDialog'
 import { useExtensionService } from '@/services/extensionService'
 import { useLitegraphService } from '@/services/litegraphService'
 import { useSubgraphService } from '@/services/subgraphService'
@@ -1068,7 +1069,7 @@ export class ComfyApp {
 
   private showMissingNodesError(missingNodeTypes: MissingNodeType[]) {
     if (useSettingStore().get('Comfy.Workflow.ShowMissingNodesWarning')) {
-      useDialogService().showLoadWorkflowWarning({ missingNodeTypes })
+      useMissingNodesDialog().show({ missingNodeTypes })
     }
   }