feat: surface localized error feedback for rejected files in ComfyHubExamplesStep

## Summary

In `src/platform/workflow/sharing/components/publish/ComfyHubExamplesStep.vue`, the `createExampleImages` function silently drops files that fail validation (non-image MIME type or exceeding `MAX_IMAGE_SIZE_MB`). Users receive no feedback explaining why their files were ignored.

## Proposed Change

Update `createExampleImages` to:
1. Detect rejected files (non-image MIME type via `f.type.startsWith('image/')` check, or oversized via `isFileTooLarge`)
2. Build a localized, actionable rejection message per file (including `file.name` and the reason)
3. Dispatch the message through the component's existing UI error channel (e.g., a toast or inline error)
4. Continue returning the valid `ExampleImage[]` array as before

Use `vue-i18n` via the Composition API (`t('...')`) for all user-facing strings.

## Context

- Raised during review of PR #10128 (ComfyHub publish wizard)
- Comment: https://github.com/Comfy-Org/ComfyUI_frontend/pull/10128#discussion_r2944032711
- Non-blocking for initial launch; deferred to a follow-up PR
- Requested by: @christian-byrne

┆Issue is synchronized with this [Notion page](https://www.notion.so/Issue-10466-feat-surface-localized-error-feedback-for-rejected-files-in-ComfyHubExamplesStep-32d6d73d36508115a438f868786d61e2) by [Unito](https://www.unito.io)