feat(ai-cover): add pack name text embedding support for FLUX.1 schnell

Commit notes

- Add embedPackName option to GenerateCoverRequest interface - Implement buildTextEmbeddingPrompt function for style-specific text rendering - Update buildCoverPrompt to append text embedding when enabled - Add output_format and guidance_scale parameters per FLUX.1 API schema - Update routes to accept and pass embedPackName parameter - Update frontend API client and query hooks with embedPackName option - Add UI toggle in AICoverGenerator for embedding pack name as visible text

The pack name can now be embedded as visible typography in the generated cover image, with style-specific rendering for abstract, photographic, and illustrated styles.

Co-authored-by: armin.naimi <[email redacted]>