test: add unit tests for resolveBlueprintIcon, resolveBlueprintSuffix, and resolveBlueprintEssentialsCategory

## Summary

Three new exported pure functions were added to `src/constants/essentialsDisplayNames.ts` in PR #10113, but no unit tests were added for them:

- `resolveBlueprintIcon(nodeName)` — derives an icon class from the blueprint prefix
- `resolveBlueprintSuffix(nodeName)` — extracts and title-cases the provider/model suffix from a blueprint name
- `resolveBlueprintEssentialsCategory(nodeName)` — returns the `EssentialsCategory` for a blueprint node, or `undefined`

The existing test file (`essentialsDisplayNames.test.ts`) only covers `resolveEssentialsDisplayName`.

## Suggested test coverage

- **`resolveBlueprintIcon`**: prefix matching → correct icon class string; non-blueprint name → `undefined`; trailing underscore stripped correctly
- **`resolveBlueprintSuffix`**: suffix title-casing (e.g. `text_to_image_flux_1` → `"Flux 1"`); no suffix → `undefined`; non-blueprint name → `undefined`
- **`resolveBlueprintEssentialsCategory`**: correct category returned for each prefix group; non-blueprint name → `undefined`; unrecognized blueprint prefix → `undefined`

## References

- PR: https://github.com/Comfy-Org/ComfyUI_frontend/pull/10113
- Comment: https://github.com/Comfy-Org/ComfyUI_frontend/pull/10113#discussion_r2945046825
- Requested by: @christian-byrne

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