convrot: add loss comparison charts (Z-Image, Mage Flow)

[bghira]

This pull request updates the Mage-Flow and Z-Image quickstart documentation across all supported languages with improved guidance and new benchmarking data for SDNQ INT8/ConvRot and SDNQ Hadamard quantization. The changes clarify recommended validation practices, provide concrete performance metrics, and explain the impact of bucket aspect ratio on compilation time and training efficiency.

Mage-Flow documentation improvements:

• Added recommendations to prefer square-crop buckets for SDNQ INT8 and ConvRot validation, with a detailed table of loss and timing results from a 100-step LoRA smoke test on H100 and L40S GPUs. Warns about compilation overhead with arbitrary aspect buckets and advises keeping the text encoder frozen. [1] [2] [3] [4] [5] [6]

Z-Image documentation improvements:

• Added new sections reporting measured SDNQ Hadamard training performance for H100 and L40S GPUs, including benchmark tables and comparison to baseline. Instructs users to treat results as reference points, not guarantees, and links to quick setup instructions. [1] [2] [3] [4] [5] [6]

No code changes were made; all updates are to documentation for clarity, reproducibility, and user guidance.