feat: add provider logo overlays to workflow template thumbnails (#8365)

## Summary

Add support for overlaying provider logos on workflow template
thumbnails at runtime.

## Changes

- **What**: 
  - Add `LogoInfo` interface and `logos` field to `TemplateInfo` type
  - Create `LogoOverlay.vue` component for rendering positioned logos
  - Fetch logo index from `templates/index_logo.json` in store
  - Add `getLogoUrl` helper to `useTemplateWorkflows` composable
  - Integrate `LogoOverlay` into `WorkflowTemplateSelectorDialog`

## Review Focus

- Logo positioning uses Tailwind classes (e.g. `absolute bottom-2
right-2`)
- Supports multiple logos per template with configurable size/opacity
- Gracefully handles missing logos (returns empty string, renders
nothing)
- Templates must explicitly declare logos - no magic inference from
models

## Dependencies

Requires separate PR in workflow_templates repo to:
1. Update `index.schema.json` with logos definition
2. Add `logos` field to templates in `index.json`

## Screenshots (if applicable)

<img width="869" height="719" alt="image"
src="https://github.com/user-attachments/assets/65ed1ee4-fbb4-42c9-95d4-7e37813b3655"
/>


┆Issue is synchronized with this [Notion
page](https://www.notion.so/PR-8365-feat-add-provider-logo-overlays-to-workflow-template-thumbnails-2f66d73d365081309236c6b991cb6f7b)
by [Unito](https://www.unito.io)

---------

Co-authored-by: Subagent 5 <subagent@example.com>
Co-authored-by: Amp <amp@ampcode.com>

src/locales/en/main.json

@@ -966,6 +966,9 @@
       "searchPlaceholder": "Search..."
     }
   },
+  "templates": {
+    "logoProviderSeparator": " & "
+  },
   "graphCanvasMenu": {
     "zoomIn": "Zoom In",
     "zoomOut": "Zoom Out",