Fix contrast in light themes

[Maxteabag]

Summary

• replace hard-coded yellow explorer matches with the active theme primary color
• replace hard-coded cyan command-mode text with the active theme primary color
• validate command text contrast across all six supported light themes
• add explorer-filter and real rendered-theme regressions

Fixes #266.

Validation

• 14 focused UI regressions passed
• rendered screenshots verified for Sqlit Light, Textual Light, Solarized Light, Catppuccin Latte, Rose Pine Dawn, and Gruvbox Light
• each primary/surface combination has at least 3:1 contrast
• structured autoreview: clean