feat: add WISE smoke task with OpenRouter image artifacts

[Luodian]

Summary

• add OpenRouter image-generation backend registration for WISE smoke usage
• add wise_smoke task + fixture and artifact-existence metric
• add a dedicated WISE smoke script for reproducible real-model image generation runs

Verification

• bash examples/models/openrouter_wise_smoke.sh
• run passed with wise_smoke_success=1
• sample log: logs/openrouter_wise_smoke/google__gemini-2.5-flash-image/20260224_000803_samples_wise_smoke.jsonl
• generated artifact: logs/openrouter_wise_outputs/wise_smoke/wise_smoke_0_0.png

Closes #1196

[Luodian]

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