feat: add Unify real-dataset smoke pipelines

[Luodian]

Summary

• add OpenRouter image-generation backend and register it for Unify generation smoke usage
• add realunify_gen_smoke task + fixture for local artifact-validation path
• add two runnable scripts: image-generation smoke and real-dataset smoke (realunify_mental_tracking, uni_mmmu_jigsaw)

Verification

• bash examples/models/openrouter_unify_real_smoke.sh
• run passed on real datasets with refreshed HF token context
• sample logs:
  • logs/openrouter_unify_real_smoke/openai__gpt-4.1-mini/20260224_000439_samples_realunify_mental_tracking.jsonl
  • logs/openrouter_unify_real_smoke/openai__gpt-4.1-mini/20260224_000439_samples_uni_mmmu_jigsaw.jsonl
• additional image artifact smoke:
  • bash examples/models/openrouter_unify_image_smoke.sh
  • realunify_gen_smoke_success=1

Closes #1194

[Luodian]

Closing: core openrouter_image_gen model backend already merged via #1198. The Unify task/script additions need a fresh PR without the duplicated model backend and formatting conflicts.