Update app chrome controls and normalize heatmap intensity to dynamic overlap maxima

[felixgollnhuber]

Summary

• Set browser metadata branding to tempoll.app for default and templated page titles
• Compact header controls for small screens using icon variants while preserving accessible labels for language, new event, and recent events
• Add mobile-icon mode to LanguageSwitcher with locale label fallback on larger screens
• Change heatmap coloring from absolute counts to relative scaling against the current maximum overlap
• Sync legend swatches with the same relative heatmap scale and add/adjust tests for accessibility and overlap-color behavior

Testing

• Not run (not requested)