Introduce an interactive Four Color Theorem demo: add FourColorComponent (template, styles, standalone component) with canvas-based grid, region generation, adjacency detection and a backtracking solver; include models for nodes/regions and grid constants. Wire up route and RouterConstants/UrlConstants, add menu entry in AlgorithmsService, and add i18n entries for English and German. Also add global color styles in styles.scss and a few minor i18n text adjustments.
