[FEATURE] Introduce quick legend

## Feature Request

### Description
Unclear if the colors represent score relative to entire table or just within a column. SAB recommendation to introduce a button that quickly explains how to interpret the table.

### Technical Details
- **Page URL**: https://www.brain-score.org/vision/leaderboard/?min_param_count=0&max_param_count=900&min_model_size=0&max_model_size=4000&min_score=0&max_score=1&min_stimuli_count=0&max_stimuli_count=51000
- **Timestamp**: 2025-11-06T12:56:27.765Z
- **User Agent**: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_7) AppleWebKit/605.1.15 (KHTML, like Gecko) Version/26.0.1 Safari/605.1.15
- **System Info**: Browser: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_7) AppleWebKit/605.1.15 (KHTML, like Gecko) Version/26.0.1 Safari/605.1.15 | Screen: 2560x1440 | Viewport: 2560x1319 | Platform: MacIntel | Language: en-US | Timestamp: 2025-11-06T12:55:42.422Z

### Current Filter State
- **Search Term**: ``
- **Visible Rows**: 480
- **Active Filters**: {
"architecture": [],
"model_family": [],
"training_dataset": [],
"task_specialization": [],
"max_param_count": 900,
"max_model_size": 4000,
"runnable_only": false,
"benchmark_regions": [],
"benchmark_species": [],
"benchmark_tasks": [],
"public_data_only": false,
"min_param_count": 0,
"min_model_size": 0,
"min_score": 0,
"max_score": 1,
"min_stimuli_count": 0,
"max_stimuli_count": 51000
}

---
*This issue was automatically generated from the Brain-Score website.*

Start at the vision leaderboard page URL in the issue and inspect the table’s color rendering and nearby controls. Add a quick legend button that explains whether colors represent scores across the entire table or within each column; done means users can find and understand that explanation.

Written by the indexing model from the issue text.